THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


THE    DIFFERENT    FORMS    OF 

FLOWERS   ON   PLANTS  OF 

THE  SAME  SPECIES 


BY 

CHARLES  DARWIN,  M.  A.,  F.  R.  S. 


WITH  ILLUSTRATIONS 


NEW    YORK 
D.   APPLETON   AND   COMPANY 

1899 


Authorized  Edition. 


TO 

PROFESSOR  ASA  GRAY 

THIS  VOLUME  IS  DEDICATED  BY  THE  AUTHOR 
AS  A   SMALL  TRIBUTE  OF  EESPECT  AND  AFFECTION. 


2033582 


PREFACE  TO  THE  REPRINT  OF  1884. 


THE  text  of  the  second  edition  has  been  left  un- 
touched, and  I  have  merely  given  an  account  (which 
does  not  pretend  to  be  complete)  of  the  progress  of  the 
subject  since  1880. 

HETEROSTYLED  PLANTS. 

C.  E.  Bessey  ('American  Naturalist/  June,  1880, 
p.  417)  made  careful  measurements  of  the  corolla,  sta- 
mens, and  style  in  a  number  of  flowers  of  Lithospermum 
longiflorum.  He  shows  that  the  length  of  corolla,  and 
especially  the  length  of  the  style,  is  very  variable.  An 
appearance  of  dimorphism  is  thus  produced;  but  meas- 
urements of  the  pollen  show  that  there  is  no  real  hetero- 
stylism. 

C.  B.  Clarke  ('  Journ.  Linn.  Soc./  xvii.  p.  159)  has 
made  the  curious  observation  that  in  Adenosacme  longi- 
folia  the  difference  between  the  long-  and  short-styled 
forms  amounts  to  what  would  usually  be  called  a  char- 
acter of  first-rate  systematic  importance.  In  the  short- 
styled  flowers,  the  stamens  are  on  the  corolla;  in  the 
long-styled,  they  are  at  its  very  base,  almost  free  from 
it.  In  this  form  the  corolla  separates  and  leaves  the 
stamens  standing  on  the  ovary. 


Ti  PREFACE  TO  THE  REPRINT  OF  1884. 

He  also  describes  two  forms  of  Randia  uliginosa, 
(i.)  having  large  sessile  flowers  with  separate  stigmas 
and  producing  a  large  fruit;  (ii.)  small  pedunculated 
flowers  with  clavate  stigmas,  and  producing  smaller 
fruit. 

C.  B.  Clarke  ('Journ.  Linn.  Soc.,'  xviii.  p.  524) 
shows  that  Macrotomia  is  dimorphic  like  Arnebia.  Mr. 
Clarke  mentions  as  one  of  the  earliest  good  notices  of 
heterostylism  that  Fischer  and  Meyer  ('Enum.  PI. 
Schrenk.,'  p.  34,  published  in  1841)  speak  of  Macro- 
tomia as  having  spccimina  longistyla  and  brevistyla. 

Breitenbach  ('Botanische  Zeitung/  1880,  p.  577) 
believes  that  the  ancestor  of  the  heterostyled  Primula 
was  homostyled.  He  grounds  his  belief  on  the  ex- 
amination of  a  large  number  of  plants  of  P.  elatior, 
Jacq.,  and  on  some  facts  connected  with  the  ontogene- 
sis of  the  flowers.  This  opinion  has  been  adversely 
criticised  by  W.  Behrens  ('  Botanisches  Centralblatt,' 
1880,  p.  1082)  and  by  Hermann  Muller  ('  Bot.  Zeitung,' 

1880,  p.  733). 

A.  Ernst  (Caracas)  ('  Nature,'  xxi.,  1880,  p.  217) 
shows  by  measurement  and  experiment  that  Melochia 
parviflora  is  heterostyled  (dimorphic). 

According  to  J.  Todd  ('  American  Naturalist,'  xv., 

1881,  p.  997),  Black  mustard  (B.  nigra)  has  two  forms 
of  flower,  differing  in  the  length  of  the  pistil ;  the  sta- 
mens being  of  approximately  the  same  length  in  the 
two  forms. 

Trelease  ('American  Naturalist,'  xvi.,  1882,  p.  13) 
describes  two  forms  of  Oxalis  violacea,  which  appear 
to  be  long-  and  short-styled  forms  of  a  trimorphic 
species.  No  mid-styled  flowers  could  be  found,  and 
Trelease  is  inclined  to  believe  that  the  species  is  di- 
morphic. 

Ig.  Urban  ('  Sitz.  Bot.  Verein,  Prov.  Brandenburg,' 


PEEFACE  TO  THE  REPRINT  OF  1884.  vii 

xxiv.,  1882)  states  that  the  Turneraceae  contain  a  large 
proportion  of  dimorphic  plants.  His  monograph  on  this 
family  I  know  only  from  the  abstract  in  the  *  Botan. 
Centralblatt,'  p.  207.  He  has  made  the  following  in- 
teresting observations : — "  In  the  Turneracese  the  dimor- 
phic species  tend  to  be  perennials,  with  conspicuous  flow- 
ers, while  the  monomorphic  species  have  smaller  flowers, 
and  are  chiefly  annuals."  He  states  that  a  tendency 
to  dimorphism  in  the  monomorphic  species  expresses 
itself  only  in  elongation  of  the  style. 

In  the  subjects  kindred  to  those  considered  in  Chap- 
ter VII,  rather  more  work  has  been  done. 

F.  Ludwig  ('Zeitschrift  f.  d.  gesam.  Naturwiss.,' 
1879,  p.  44)  describes  three  plant-forms  in  Plantago 
lanceolata. 

1.  Hermaphrodites  with  white  anthers. 

2.  Semi-females,  with  small  shrivelled  yellow  an- 
thers, containing  a  small  quantity  of  pollen,  of  which 
many  grains  are  bad. 

3.  Purely  female  form. 

Ludwig  has  noticed  the  tendency  described  by  Del- 
pino  to  entomophily  in  Plantago,  the  flowers  being  often 
fairly  conspicuous,  and  are  visited  by  insects. 

Ludwig  draws  some  interesting  general  conclusions 
on  Gynodioecious  plants. 

1.  They  are  all  more  or  less  dichogamic. 

2.  In  the  protandrous  forms  the  females  are  more 
numerous  at  the  beginning  of  the  season.     In  the  pro- 
togynous  forms  the  reverse  is  the  case. 

3.  Abortive  anthers  often  degrade  into  perianth  seg- 
ments. 

4.  He  confirms  the  received  opinion  that  female  flow- 
ers are  smaller  than*  hermaphrodites. 

He  discusses  the  origin  of  dioeciousness,  assigning 


viii          PREFACE  TO  THE  REPRINT  OF  1884. 

the  first  rank  in  the  chain  of  causes  to  dichogamy.  Simi- 
lar views  are  given  in  the  present  edition,  p.  283,  in 
connection  with  observations  by  Hildebrand. 

In  a  subsequent  paper  ('Botan.  Centralblatt/  1880, 
iv.  p.  829)  he  describes  a  similar  gynodioecious  condi- 
tion in  some  Stellarias  and  Cerastiums.  Here  there 
are  pure  female,  semi-female,  and  hermaphrodite  plants, 
the  flowers  of  the  female  form  being  smaller  than  those 
of  the  others.  This  distribution  of  sex  he  calls  "  gyno- 
dimorphism,"  a  condition  which  he  describes  ('Bot. 
Centralblatt,'  1880,  p.  1021)  as  occurring  in  Arenaria 
ciliata  and  Alsine  verna. 

F.  Ludwig  ('Kosmos/*  1880-81,  viii,  357)  de- 
scribes two  forms  of  Erodium  cicutarium.  The  first, 
which  is  distinguished  by  having  nectar-guides,  is  pro- 
tandrous,  and  adapted  for  fertilisation  by  insects.  The 
second  form  is  weakly  protogynous  and  autogamic. 
This  form  has  no  nectar-guides,  and  the  petals  are  usu- 
ally shed  during  the  day  on  which  the  flowers  open.  It 
resembles  E.  moschatum,  which  is  homogamic  (or  weak- 
ly protogynous).  The  first  form  is  more  like  E.  macro- 
denum,  which  is  markedly  protandrous,  and  where  auto- 
gamy is  impossible. 

Hermann  Miiller  ('Nature/  xxiii.  p.  337,  1881) 
has  shown  that  Syringa  persica  is  gynomonrecious,  hav- 
ing on  the  same  inflorescence  a  majority  of  hermaphro- 
dite flowers  of  large  size,  and  a  minority  of  small-sized 
females. 

Stellaria  glauca  and  Sherardia  arvensis  are  gyno- 
dicecious. 

H.  Miiller  has  also  written  an  important  paper  on 
Centaurea  jacea  ('Kosmos/  x.,  and  'Nature,'  xxv.)  in 
which  he  publishes  his  change  of  opinion  as  to  the  origin 

•See  also  'Irmischia,'  1881,  No.  1,  and  'Bot.  Centralblatt,'  xii.  p. 
83,  and  viii.  p.  87. 


PREFACE  TO  THE  REPRINT  OF  1884.  ix 

of  gynodiceciousness.  Three  different  forms  occur,  but 
on  any  given  plant  the  flowers  are  of  one  kind.  There 
is  a  normal  hermaphrodite  form,  and  two  divergent 
forms  which  are  practically  male  and  female,  and  which 
are  distinguished  from  the  hermaphrodite  form  by  hav- 
ing conspicuous  sexless  ray-florets ;  of  the  two,  the  male 
flowers  are  the  more  conspicuous.  The  female  florets 
have  shrunken  anthers  devoid  of  pollen ;  the  male  florets 
have  pistils  which  do  not  open,  and  are  therefore  func- 
tionless.  Numerous  gradational  forms  exist  which  ren- 
der the  whole  case  especially  instructive,  and  it  was  a 
study  of  these  gradations  which  induced  Miiller  to  give 
up  his  theory  of  gynodicecious  plants.  Miiller  formerly 
explained  the  origin  of  gynodireciousness  by  supposing 
that  those  flowers  which  are  smaller  and  less  conspicu- 
ous than  the  average  tend  to  be  visited  last  by  insects, 
so  that  their  pollen  is  useless.  In  Centaurea  the  reduc- 
tion of  anthers  is  found  beginning  in  flower-heads  which 
are  not  less  conspicuous  than  the  average.  Miiller  there- 
fore gives  up  his  former  theory  and  agrees  with  the  view 
proposed  by  my  father.* 

Potonie  ('  Sitzb.  d.  Ges.  Naturforsch.  Freunde  zu 
Berlin,'  1880,  p.  85,  quoted  in  the  '  Bot.  Zeitung,'  1880, 
p.  749)  believes  that  in  the  gynodirecious  Salvia  praten- 
sis  the  existence  of  a  female  form  serves  to  ensure  fer- 
tilisation by  a  distinct  plant. 

But  H.  Miiller  ('Bot.  Zeitung/  1880,  p.  749)  shows 
that  in  the  hermaphrodites,  bees  commonly  visit  the 
lower  and  temporarily  female  flowers  before  passing  on 
to  the  upper  male  flowers,  and  that  this  ensures  cross- 
fertilisation  between  different  plants. 

Solms-Laubach  ('Abhand.  K.  Gesell.  Wiss.  Gb't- 
tingen,'  xxviii.,  and  'Kosmos,'  1881)  has  given  in  his 

*  A  short  paper  by  H.  Muller  on  gynodiceciousness  in  the  genua 
Dianthus,  appeared  in  'Nature,'  1881,  xxiv. 


x  PBEFACE  TO  THE  EEPRINT  OP   1884. 

valuable  work  on  caprification  an  account  of  the  relation 
of  the  sexes  in  the  cultivated  fig  and  the  caprificus. 

HETERANTHY. 

The  existence  of  different  kinds  of  anthers  in 
homostyled  flowers  is  of  interest  as  bearing  on  hetero- 
stylism. 

F.  Ludwig  (<Bot.  Centralblatt/  1880,  pp.  246  and 
1210)  gives  an  account  of  the  heteranthy  of  Plantago 
major,  of  which  two  forms  exist,  one  with  brown,  the 
other  with  yellow  anthers;  the  latter  plants  are  much 
rarer  than  the  brown-anthered  form.  In  another  com- 
munication to  the  same  journal  (1880,  p.  861),  he  de- 
scribes the  heteranthy  of  Poterium  sanguisorba,  and 
of  a  number  of  grasses,  e.  g.  Lolium  dactylis,  Festuca, 
Air  a. 

F.  Miiller  ('Nature,'  xxiv.,  1881,  p.  307)  has  made 
the  curious  observation  that  in  the  Melastomaceous 
Heeria,  sp.,  there  are  two  sets  of  anthers:  (1)  yellow 
ones  serving  as  plunder  to  bees;  (2)  red  ones  so  placed 
as  to  subserve  cross-fertilisation. 

H.  Miiller  ('  Nature/  1882,  p.  30)  showed  that  in 
Tinnantia  undat  (Commelynacese),  as  in  Heeria,  two 
sets  of  anthers  exist ;  one  set  which  attract  pollen-seek- 
ing insects,  the  other  which  cover  the  insect  with  pollen. 
The  upper  stamens  have  yellow  tufts  of  hair,  which 
(as  in  Tradescantia)  serve  as  supports  for  visiting  in- 
sects. The  pollen-grains  are  smaller  in  the  upper  sta- 
mens. In  Commclyna  coslestis  and  communis  there  is 
somewhat  similar  arrangement. 

In  a  species  of  Melastoma,  which  has  also  two  sets 
of  stamens,  H.  0.  Forbes  ('Nature/  1882,  p.  386)  saw 
bees  going  straight  to  the  yellow  stamens,  i.  e.  to  those 
which  serve  as  an  attraction.  The  yellow  anthers  have 
the  smaller  pollen-grains,  but  those  from  the  other  set 


PREFACE  TO  THE  REPRINT  OF  1884.  xi 

of  anthers  were  the  only  ones  seen  to  exsert  tubes  in 
the  stigmas. 

J.  E.  Todd  ('American  Naturalist/  xvi.,  1882,  p. 
281)  gives  a  curious  account  of  Solanum  rostratum, 
in  which  the  pollen  for  fertilisation  is  the  product  of 
a  single  long-curved  anther;  while  the  four  other  an- 
thers are  small,  and  serve  to  supply  pollen  to  the  bees 
visiting  the  flower.  The  stigma  is  so  placed  that  it 
receives  pollen  from  the  part  of  the  bee  dusted  by  the 
long  anther. 

CLEISTOGAMIC  FLOWERS. 

According  to  P.  Ascherson  ('  Bulletin  Soc.  Linn,  de 
Paris/  1880,  p.  250),*  Helianthemum  salicifolium  was 
shown  by  LinnaBus  to  produce  ripe  seed  from  closed 
flowers.  Ascherson  describes  the  cleistogamic  flowers 
of  H.  Kaliiricum  and  H.  Lippii  y.  micranihum,  Boiss. 
Schweinfurth  is  given  as  authority  for  the  existence  of 
cleistogamic  flowers  in  Salvia  lanigera.  The  following 
species  are  said  to  be  "  often  cleistogamic  "  :  Lamium 
amplexicaule,  Juncus  bufonius,  Ajuga  Iva,  Campanula 
dimorphantha. 

In  a  second  paper  ('  Sitz.  d.  Gesch.  Naturf.  Freunde 
zu  Berlin/  1880,  p.  97,  quoted  in  the  <Bot.  Centralblatt') 
Ascherson  gives  a  further  account  of  the  cleistogamy 
of  Helianthemum  Kahiricum.  The  flowers  are  open 
in  the  early  morning,  so  that  cross-fertilisation  is  possi- 
ble; the  petals  fall  off  in  the  course  of  the  day,  and 
the  sepals  closely  embrace  the  stamens  and  pistils,  and 
thus  convert  the  flower  into  a  cleistogamic  one. 

Baron  E.  Eggers  (<Bot.  Centralblatt/  1881,  viii.  p. 
57)  states  that  Sinapis  arvensis,  when  grown  in  the 
West  Indies,  produces  cleistogamic  flowers. 

*  As  abstracted  in  the  '  Bot.  Centralblatt.' 


xii  PREFACE  TO  THE  REPRINT  OF  1884. 

The  following  Acanthacese  have  cleistogamic  flow- 
ers: Stenandrium  rupestre,  Didipetra  assurgens,  Ste- 
monacanthus  coccineus,  Dianthera  sessilis,  Blechum 
Brownei. 

Among  other  families:  Erithalis  fruticosa  (Eubia- 
cece),  Polystacliya  luteola,  are  also  cleistogamic. 

The  curious  flowers  of  Pavonia  hastata  are  described 
by  E.  Heckel  ('  Comptes  rendus/  Ixxxix.  p.  609).  This 
species  has  cleistogamic  flowers,  which  chiefly  differ 
in  appearance  from  the  perfect  flowers,  in  having  no 
nectar-guides;  there  are,  as  usual,  no  nectaries.  The 
pollen  is  entomophilous  in  character,  and  it  is  said 
that  the  tubes  are  protruded  while  the  pollen  is  in  the 
anthers. 

F.  Ludwig  (<Bot.  Centralblatt/  1880,  p.  861)  men- 
tions Plantago  virginica  as  producing  under  cultivation 
only  cleistogamic  flowers. 

F.  Miiller  ('  Nature,'  xix.,  1879,  p.  463)  shows  that 
the  curious  submerged  Podostomaceae  of  Brazil  produce 
flowers  which  are  probably  cleistogamic. 

Solms-Laubach  ('Gb'ttingen  Nachrichten/  June, 
1882)  has  written  an  interesting  paper  on  Heteranthera, 
a  plant  belonging  to  the  Pontedereacea?.  He  describes 
the  cleistogamy  of  some  species  of  the  genus,  and  points 
out  that  the  form  and  distribution  of  the  cleistogamic 
flowers  serve  as  a  specific  character,  without  which  H. 
callafolia  could  not  be  distinguished  from  H.  Kotsch- 
yana. 

FRANCIS  DARWIN. 

Jan.,  1884. 


PKEFACE  TO  THE  SECOND  EDITION. 


SINCE  the  publication  of  the  first  edition  of  this 
book  in  1877,  several  articles  have  appeared  on  the  sub- 
jects therein  discussed,  and  many  letters  have  been  re- 
ceived by  me.  I  will  here  briefly  state  their  nature, 
as  an  aid  to  any  one  who  may  afterwards  pursue  the 
same  subjects.  The  text  has  been  left  as  it  originally 
appeared,  excepting  that  a  few  errors  have  been  cor- 
rected. 

Dr.  A.  Ernst  has  proved  in  the  clearest  manner 
'(' Nature/  Jan.  1,  1880,  p.  217)  that  Melochia  parvi- 
folia,  which  is  a  common  plant  near  Caracas,  is  hetero- 
styled.  The  pollen-grains  differ  in  the  usual  manner 
in  size  in  the  two  forms,  as  do  the  papillae  on  their  stig- 
mas. The  illegitimate  unions,  especially  when  pollen 
from  the  same  flower  was  employed,  were  much  less  fer- 
tile than  the  legitimate  ones.  A  new  family,  the  Bytt- 
neriaceae,  is  thus  added  to  those  including  heterostyled 
plants. 

Errara  and  Gevaert  have  published  a  paper  on  the 
heterostylism  of  Primula  elatior,  in  '  Bull.  Soc.  E.  Bot. 
Belg.,'  torn,  xvii.,  1879. 

I  have  quoted  (p.  100)  Dr.  Alefeld's  statement  that 
none  of  the  American  species  of  Linum  are  heterostyled. 
This  statement  was  disputed  by  Kuhn  ('Bot.  Zeit./ 
1866,  p.  201),  but  has  since  been  confirmed  by  Dr.  Ign. 

xiii 


^  PREFACE. 

Urban/  in '  Linnsea/  B.  vii.  p.  621.  Mr.  Meehan  ('  Bull. 
Torrey  Bot.  Club/  vol.  vi.  p.  189)  has  endeavoured  to 
throw  doubts  on  my  observations  on  the  sterility  of  the 
forms  of  L.  perenne  when  fertilised  with  their  own-form 
pollen,  because  a  plant  from  Colorado  yielded  seed  when 
growing  by  itself ;  but  as  might  have  been  expected,  and 
as  is  sufficiently  clear  from  the  remarks  of  a  well-known 
reviewer  in  the  '  American  Journal  of  Science/  Mr. 
Meehan  mistook  L.  Lewisil,  which  is  not  heterostyled, 
for  L.  perenne. 

In  the  Boragineae,  Lithospermum  canescens  differs, 
according  to  Mr.  Erwin  F.  Smith  ('  Bot.  Gazette/ 
United  States,  vol.  iv.,  1879,  p.  168),  from  the  hetero- 
styled  species  of  the  same  genus  by  occasionally  present- 
ing a  mid-styled  form,  which  has  a  short  pistil  like  that 
of  the  short-styled,  and  short  stamens  like  those  of  the 
long-styled  form.  All  the  forms  seem  variable,  and  the 
whole  case  requires  further  investigation. 

Mr.  Alex.  S.  Wilson  informs  me  that  on  comparing 
the  pollen-grains  from  a  long-styled  plant  of  Erytlircea 
centaurium  with  those  from  some  short-styled  plants 
from  the  island  of  Arran,  they  differed  in  size  and 
shape,  as  in  the  case  of  the  undoubtedly  heterostyled 
Menyanthcs  trifoliata,  a  member  of  the  same  family  of 
the  Gentianeae.  I  had  myself  formerly  observed  that 
the  flowers  on  different  plants  differed  much  in  struc- 
ture, but  could  not  make  out  that  they  presented  two 
distinct  forms. 

The  Rubiacese  contain  many  more  heterostyled 
plants  than  any  other  family,  and  several  additional 
cases  can  now  be  added.  Mr.  C.  B.  Clarke  has  been 

kind  as  to  send  me  sketches  made  in  India  of  two 

extremely   distinct   forms    of   Adenosacme    longifolia. 

e  remarks  "that  the  peculiarity  of  the  case  is  not 

the  difference  in  the  length  of  the  style  and  stamens 


PREFACE.  XV 

in  the  two  forms,  but  the  extreme  difference  in  the 
point  of  insertion  of  the  stamens."  A  mid-styled  form 
exists  having  a  short  pistil  and  short  stamens  seated  on 
the  same  level,  only  a  little  way  up  the  tube  of  the 
corolla.  Mr.  Clarke  adds  that  heterostylism  is  quite 
common  in  the  Coffee  tribe.  Mr.  Hiern,  in  his  obser- 
vations on  the  Eubiaceae  of  tropical  Africa  ('  Journal 
Linn.  Soc.  Bot./  vol.  xvi.,  1877,  p.  252),  remarks  that 
dimorphism  occurs  commonly,  or  at  least  in  some  spe- 
cies, in  four  or  five  genera  in  the  tribe  of  Hedyotideae. 
Mr.  M.  S.  Evans  states  ('  Nature,'  Sept.  19,  1878,  p. 
543)  that  in  Natal  there  is  a  heterostyled  Eubiaceous 
plant,  which  occasionally,  though  rarely,  presents  a 
third  form,  and  in  this  the  pistil  and  stamens  are  of 
equal  length  and  both  are  exserted  from  the  mouth  of 
the  corolla.  He  adds  that  he  has  found  four  other 
heterostyled  dimorphic  plants,  and  one  of  these  is  a 
monocotyledon. 

Lastly,  I  have  given  (p.  135)  Bouvardia  leiantha  as 
doubtfully  heterostyled;  Mr.  Bailey  has  now  sent 
me  dried  specimens,  and  as  far  as  the  lengths  of  the 
pistil  and  stamens  are  concerned  the  species  is  clearly 
heterostyled;  but  no  difference  could  be  detected  in 
the  size  of  the  pollen-grains;  so  the  case  must  remain 
doubtful. 

With  respect  to  trimorphic  heterostyled  plants,  Dr. 
Koehne,  who  has  described  the  Lythraceae  of  Brazil, 
has,  with  great  kindness,  sent  me  a  long  account  of 
them.  He  knows  twenty-one  species  which  are  hetero- 
styled, and  340  which  are  homostyled.  He  informs 
me  that  Lythrum  thymifolia  is  not  heterostyled,  and 
that  I  must  have  received  some  other  species  under 
this  name.  There  are  many  dimorphic  species  in 
America.  Pemphis  acidula  is  distinctly  dimorphic,  so 
are  some  species  of  Eotala  and  Nesaea;  thus  two  new 


xvj  PREFACE. 

heterostyled  genera  are  added  to  the  family.  Dr.  Koehne 
does  not  believe  that  any  species  of  Lagerstrcemia  is,  or 
has  been,  heterostyled  and  trimorphic.  He  has  also 
sent  me  an  outline  of  an  important  view,  well  worth  fol- 
lowing out,  namely,  that  heterostylism  has  arisen 
through  the  modification  of  plants  which  were  tend- 
ing to  become  polygamous  or  dioecious. 

It  is  stated  at  p.  187  that  Mr.  Leggett  felt  some 
doubt  whether  Pontederia  cordata  was  trimorphic  and 
heterostyled;  but  he  has  since  written  to  me  that  his 
doubts  are  removed :  see  also  to  this  effect,  in  '  Bull. 
Torrey  Bot.  Club/  vol.  vi.,  1877,  p.  170.  All  three 
forms  of  this  Pontederia  appear  to  be  highly  variable. 
He  informs  me  that  humble-bees  are  the  fertilisers. 

With  respect  to  the  origin  of  the  dioecious  state, 
which  is  discussed  in  the  beginning  of  the  seventh 
chapter,  Hermann  Miiller  has  given  some  interesting 
remarks  in  *  Kosmos,'  1877,  p.  290.  The  same  author 
shows  (Ibid.,  p.  130)  that  Valeriana  dioica  exists  under 
four  forms  closely  allied  to  the  four  presented  by 
Khamnus,  as  described  in  this  same  chapter.  It  is 
much  to  be  desired  that  some  one  should  experimentise 
on  these  forms  and  make  out  their  meaning.  Bernet 
has  published  ('Bull.  Soc.  Bot.  France,'  torn,  xxv., 
1878)  a  paper  entitled,  'Disjunction  des  sexes  dans 
VEuonymus  Europceus,'  which  may  be  compared  with 
my  observations  on  the  same  plant.  I  have  stated 
at  p.  297  that  I  could  never  find  an  hermaphrodite 
plant  of  the  common  holly,  but  according  to  Mr. 
Hibberd  ('  Gard.  Chron.,'  1877,  pp.  39  and  776)  such 
occur  among  the  many  cultivated  varieties.  The  evi- 
dence, however,  is  far  from  conclusive,  for  it  does  not 
appear  that  Mr.  Hibberd  ever  observed  under  the  mi- 
croscope pollen  taken  from  a  plant  known  to  produce 
berries.  Trees  of  Juglans  cinerea  in  the  U.  States  are 


PREFACE.  xvii 

monoecious,  and  like  those  of  J.  regia  consist  of  two 
sets,  one  being  proterandrous  and  the  other  proterogy- 
nous  (Mr.  C.  G.  Pringle,  in  '  Bot.  Gazette,'  vol.  iv.,  1879, 
p.  237) ;  and  thus  the  cross-fertilisation  of  distinct  trees 
is  insured.  Mr.  Alex.  S.  Wilson  informs  me  that  Silene 
inftata  is  polygamous  on  Ben  Lawers,  as  he  found  her- 
maphrodite, male  and  female  plants.  The  case  is  here 
mentioned  because  the  flowers  on  the  females  are  small 
like  those  on  the  females  in  the  gyno-dioecious  sub-class. 
In  an  article  in  the  '  Bull.  Torrey  Bot.  Club,'  July,  1871, 
this  Silene  is,  however,  said  to  be  gyno-direcious.  As- 
paragus officinalis  is  also  polygamous,  and  the  female 
flowers  are  about  half  the  size  of  the  male  ones;  see 
'Gard.  Chron.,'  May  25, 1878;  also  Breitenbach,  in  'Bot. 
Zeitung,'  1878,  p.  163. 

Several  cases  can  now  be  added  to  my  list  of  gyno- 
dicecious  plants,  or  those  which  exist  as  hermaphrodite 
and  female  individuals;  namely,  according  to  Mr. 
Whitelegge  ('Nature,'  Oct.  3,  1878,  p.  588),  Stachys 
germanica,  Ranunculus,  acris,  repens,  and  bulbosus. 
H.  Miiller  found  on  the  Alps  ('Nature,'  1878,  p.  516) 
Geranium  sylvaticum  and  Dianthus  superbus  in  this 
state,  and  the  female  flowers  of  the  former  were  of 
small  size.  So  it  is  with  Salvia  pratensis,  as  he  informs 
me  in  a  letter.  I  have  received  an  additional  account 
of  Plantago  lanceolata  being  gyno-dioscious  in  England ; 
and  Dr.  F.  Ludwig  of  Greiz  has  sent  me  a  description 
of  no  less  than  five  forms  of  this  plant  which  graduate 
into  one  another;  the  intermediate  forms  being  com- 
paratively rare,  whilst  the  hermaphrodite  form  is  the 
commonest.  With  respect  to  the  steps  by  which  a  gyno- 
dicecious  condition  has  been  gained,  H.  Miiller  main- 
tains by  many  able  arguments  ('Kosmos,'  1877,  pp.  23, 
128,  and  290)  the  view  which  he  has  propounded;  and 
several  botanists  think  it  more  probable  than  the  one 


xviii 


PREFACE. 


advanced  by  me;  see,  for  instance,  'Journal  of  Botany,' 
Dec.  1877,  p.  376. 

I  have  stated  (p.  13)  that  after  inquiring  from  sev- 
eral botanists  I  could  hear  of  no  instance,  except  a  doubt- 
ful one,  of  plants  in  an  andro-dioecious  condition,  or  ex- 
isting as  hermaphrodite  and  male  individuals.  But  II. 
Miiller  ('Nature,'  Sept.  12,  1878,  p.  159)  has  found  on 
the  Alps  Veratrum  album,  Dryas  octopetala,  and  Geum 
reptans  in  this  condition.  It  is  an  interesting  fact  that 
the  corollas  of  the  male  flowers  are  not  diminished  in 
size  like  those  of  the  females  of  gyno-dioecious  plants. 
Asa  Gray  has  also  reason  to  suspect  that  Diospyros  vir- 
giniana  may  be  andro-dioecious. 

The  eighth  chapter  is  devoted  to  cleistogamic  flowers, 
and  I  have  struck  out  of  the  list  there  inserted  four 
genera,  owing  to  information  given  me  by  Mr.  Bentham 
and  Asa  Gray.  On  the  other  hand,  fifteen  genera  have 
been  added.  Mr.  Bentham  informs  me  that  the  S. 
American  Trifolium  polymorphism  produces  true  cleis- 
togamic flowers.  Dalibarda,  Milium,  and  Yilfa  have 
been  added  to  the  list  on  the  authority  of  A.  Gray  in  a 
review  of  this  book  in  the  '  American  Journal  of  Sci- 
ence.' The  cleistogamic  flowers  of  Danthonia  are  de- 
scribed by  Pringle,  in  the  '  American  Naturalist,'  1878, 
p.  248,  and  those  of  another  Gramineous  genus,  Di- 
plachne,  by  Ascherson,  in  '  Sitzungsb.  der  Gesell.  Natur. 
Freunde,  Berlin,'  Dec.  21,  1869.  Krascheninikovia  has 
been  added  from  some  remarks  made  in  '  Journal  of 
Botany,'  1877,  p.  377.  Batalin  has  published  an  essay 
('Act.  Hort.  Petropol/  torn.  v.  fasc.  2,  1878),  'Kleisto- 
gamische  Bliithen  der  Caryophylleen,'  namely,  on  Ceras- 
tium  and  Polycarpon.  F.  Ludwig  has  described  the  cleis- 
togamic flowers  of  Collomia  grandiflora  in  '  Sitzb.  Bot. 
Vereins.  Brandenburg.'  Aug.  25,  1876 :  see  also  on  same 
subject  Scharlok,  in  'Bot.  Zeitung,'  1878,  p.  641.  A. 


PREFACE.  xix 

Grisebach  has  discussed  fully  ('  Nachrichten  k.  Gesell. 
der  Wissen.  zu  Gottingen/  June  1,  1878)  the  cleisto- 
gamic  flowers  produced  by  Cardamine  chenopodifolia, 
which  bury  themselves  in  the  ground.  See  also  on  same 
subject  Drude,  in  '  Sitzb.  der  Versamml.  d.  Naturf .  in 
Cassel,'  1878.  From  a  note  received  from  Dr.  Koehne, 
it  is  clear  that  Ammannia  latifolia  bears  cleistogamic 
flowers.  According  to  Mr.  Bessey  (the  '  American 
Naturalist/  1878,  p.  69)  this  is  likewise  the  case  with 
Lithospermum  longiflorum.  Three  genera  of  Orchidea? 
have  been  added  to  the  list,  from  information  given  me 
by  Mr.  Spencer  Moore  and  from  some  remarks  in 
'  Journal  of  Botany,'  1877,  p.  377.  Lastly,  Mr.  Bennett 
has  published  ('  Journ.  Linn.  Soc.  Bot.,'  No.  101,  1879) 
some  additional  "  notes  on  cleistogamic  flowers,"  chiefly 
on  those  of  Viola  and  Impatiens. 

With  respect  to  the  statement  (p.  328)  on  the  author- 
ity of  Mr.  Wallis,  that  Drosera  rotundifolia  opens  its 
flowers  only  early  in  the  morning,  Mr.  Conybeare  in- 
forms me  that  he  once  saw  in  Cornwall,  at  2  p.  M.,  the 
ground  "  starred  over  with  the  fully-expanded  flowers 
of  this  plant."  He  had  previously  long  endeavoured  to 
find  a  plant  with  open  flowers. 

The  number  of  species  in  which  pods  produced  by 
cleistogamic  flowers  bury  themselves  in  the  ground  is 
remarkable.  I  have  attributed  (p.  337)  this  action  to 
the  advantage  gained  by  their  protection  from  various 
enemies,  and  much  may  be  said  in  favour  of  this  view; 
but  Mr.  W.  Thiselton  Dyer  in  an  interesting  article 
('Nature,'  April  4,  1878,  p.  446)  has  called  attention 
to  some  observations  made  long  ago  by  Mr.  Bentham 
('  Catalogues  des  Plantes  indig.  des  Pyrenees,'  1826,  p. 
85)  on  the  fruiting  of  Helianthemum  prostratum.  He 
believes,  as  does  Mr.  Dyer,  that  the  capsules  of  this 
Helianthemum  and  some  other  plants  (for  instance,  of 


xx  PREFACE. 

Cyclamen)  are  kept  cool  and  moist  by  being  laid  on  the 
ground ;  they  thus  mature  more  slowly,  and  are  enabled 
to  grow  to  a  larger  size.  In  this  simple  action  we  prob- 
ably see  the  first  step  to  the  further  development  of  the 
process,  and  to  the  capsules  burying  themselves  beneath 
the  surface.  In  some  cases  the  difference  between  the 
subaerial  and  subterranean  pods  on  the  same  plant  and 
both  produced  by  cleistogamic  flowers  is  extraordinary: 
Mr.  Meehan  sent  me  three  subterranean  pods  of  Amplii- 
carpcea  monoica,  each  containing  a  single  large  seed ;  and 
my  own  plants  produced  several  subaerial  pods,  each 
containing  from  one  to  three  small  seeds.  These  latter 
weighed  on  an  average  only  -fa  of  the  subterranean  seeds  ! 
This  difference,  however,  is  not  quite  accurate,  as  the 
coats  of  the  subterranean  pods  adhered  so  firmly  to  the 
seeds  that  they  were  not  removed  and  were  weighed 
with  them;  but  from  their  thinness  and  lightness  they 
could  not  have  much  affected  the  result. 


CONTENTS. 


PREFACE  TO  REPRINT  OF  1884 Page  v 

PREFACE xiii 

INTRODUCTION  .  .  ....    1-13 


CHAPTER    I. 
HETEROSTYLED  DIMORPHIC  PLANTS  :  PRIMULACE^E. 

Primula  veris  or  the  Cowslip— Differences  in  structure  between  the 
two  forms — Their  degrees  of  fertility  when  legitimately  and 
illegitimately  united — P.  elatior,  vulgaris,  Sinensis,  auricula, 
&c. — Summary  on  the  fertility  of  the  heterostyled  species  of 
Primula — Homostyled  species  of  Primula — Hottonia  palustris 
— Androsace  Vitalliana Page  14-54 

CHAPTER    II. 

HYBRID  PRIMULAS. 

The  Oxlip  a  hybrid  naturally  produced  between  Primula  veris  and 
vulgaris — The  differences  in  structure  and  function  between 
the  two  parent-species — Effects  of  crossing  long-styled  and 
short-styled  Oxlips  with  one  another  and  with  the  two  forms 
of  both  parent-species — Character  of  the  offspring  from  Ox- 
lips  artificially  self-fertilised  and  cross-fertilised  in  a  state  of 
nature — Primula  elatior  shown  to  be  a  distinct  species — 
Hybrids  between  other  heterostyled  species  of  Primula — Sup- 
plementary note  on  spontaneously  produced  hybrids  in  the 
genus  Yerbascurn 55-80 


xxi;  CONTENTS. 

CHAPTER    III. 

HETEEOSTYLED  DIMORPHIC  PLANTS— continued. 

Linum  grandiflorum,  long-styled  form  utterly  sterile  with  own- 
form  pollen— Linura  perenne,  torsion  of  the  pistils  in  the 
long-styled  formal  one— Homostyled  species  of  Liuum— Pul- 
monaria  officinalis,  singular  difference  in  self -fertility  between 
the  English  and  German  long-styled  plants— Pulinonaria 
angustifolia  shown  to  be  a  distinct  species,  long-styled  form 
completely  self-sterile— Polygon um  fagopyrum— Various  other 
heterostyled  genera— Rubiaceae— Mitchella  repens,  fertility  of 
the  flowers  in  pairs— Houstonia— Faramea,  remarkable  differ- 
ence in  the  pollen-grains  of  the  two  forms ;  torsion  of  the 
stamens  in  the  short-styled  form  alone ;  development  not  as 
yet  perfect— The  heterostyled  structure  in  the  several  Rubi- 
aceous  genera  not  due  to  descent  in  common  .  Page  81-136 

CHAPTER    IV. 

HETEEOSTYLED  TEIMORPHIC  PLANTS. 

Lythrum  salicaria — Description  of  the  three  forms — Their  power 
and  complex  manner  of  fertilising  one  another — Eighteen  dif- 
ferent unions  possible — Mid-styled  form  eminently  feminine 
in  nature — Lythrum  Graefferi  likewise  trimorphic — L.  thymi- 
folia  dimorphic — L.  hyssopifolia  homostyled — Nesaea  verti- 
cillata  trimorphic— Lagerstrcemia,  nature  doubtful— Oxalis, 
trimorphic  species  of— 0.  Valdiviana— 0.  Regnelli,  the  illegiti- 
mate unions  quite  barren — 0.  speciosa — 0.  sensitiva — Homo- 
styled  species  of  Oxalis— Pontederia,  the  one  monocotyledonous 
genus  known  to  include  heterostyled  species  .  .  137-187 

CHAPTER  V. 

ILLEGITIMATE  OFFSPRING  OF  HETEEOSTYLED  PLANTS. 

Illegitimate  offspring  from  all  three  forms  of  Lythrum  salicaria— 
Their  dwarfed  stature  and  sterility,  some  utterly  barren,  some 


CONTENTS.  sxiii 

fertile— Oxalis,  transmission  of  form  to  the  legitimate  and 
illegitimate  seedlings — Primula  Sinensis,  illegitimate  offspring 
in  some  degree  dwarfed  and  infertile — Equal-styled  varieties 
of  P.  Sinensis,  auricula,  farinosa,  and  elatior — P.  vulgaris, 
red-flowered  variety,  illegitimate  seedlings  sterile — P.  veris, 
illegitimate  plants  raised  during  several  successive  genera- 
tions, their  dwarfed  stature  and  sterility — Equal-styled  varie- 
ties of  P.  veris — Transmission  of  form  by  Pulmonaria  and 
Polygonum — Concluding  remarks — Close  parallelism  between 
illegitimate  fertilisation  and  hybridism  .  .  Page  188-244 


CHAPTER    VI, 

CONCLUDING  REMARKS  ON  HETEROSTYLED  PLANTS. 

The  essential  character  of  heterostyled  plants— ^Summary  of  the 
differences  in  fertility  between  legitimately  and  illegitimately 
fertilised  plants — Diameter  of  the  pollen-grains,  size  of  an- 
thers and  structure  of  stigma  in  the  different  forms — Affinities 
of  the  genera  which  include  heterostyled  species — Nature  of 
the  advantages  derived  from  heterostylism — The  means  by 
which  plants  become  heterostyled  —  Transmission  of  form 
— Equal-styled  varieties  of  heterostyled  plants — Final  re- 
marks .  .  245-277 


CHAPTER    VII. 

POLYGAMOUS,  DICECIOUS,  AND  GYNO-DICECIOUS  PLANTS. 

The  conversion  in  various  ways  of  hermaphrodite  into  dioecious 
plants — Heterostyled  plants  rendered  dioecious — Rubiaceae — 
Verbenaceae  —  Polygamous  and  sub-dioecious  plants — Euo- 
nymus — Fragaria — The  two  sub-forms  of  both  sexes  of  Rham- 
nus  and  Epigtea — Ilex— Gyno-dicecious  plants— Thymus,  dif- 
ference in  fertility  of  the  hermaphrodite  and  female  individuals 
— Satureia — Manner  in  which  the  two  forms  probably  origi- 
nated— Scabiosa  and  other  gyno-dio3cious  plants — Difference  in 
the  size  of  the  corolla  in  the  forms  of  polygamous,  dioecious, 
and  gyno-dioecious  plants 278-308 


CONTENTS. 

CHAPTER   VIII. 

CLEISTOQAMIC  FLOWERS. 

General  character  of  cleistogamic  flowers — List  of  the  genera  pro- 
ducing such  flowers,  and  their  distribution  in  the  vegetable 
series — Viola,  description  of  the  cleistogamic  flowers  in  the 
several  species ;  their  fertility  compared  with  that  of  the  per- 
fect flowers— Oxalis  acetosella— 0.  sensitiva,  three  forms  of 
cleistogamic  flowers — Vandellia  —  Ononis — Impatiens — Dro- 
sera — Miscellaneous  observations  on  various  other  cleistogamic 
plants— Anemophilous  species  producing  cleistogamic  flowers 
— Leersia,  perfect  flowers  rarely  developed — Summary  and  con- 
cluding remarks  on  the  origin  of  cleistogamic  flowers — The 
chief  conclusions  which  may  be  drawn  from  the  observations  in 
this  volume Page  309-344 


INDEX 345-351 


THE 

DIFFERENT  FORMS  OF  FLOWERS 

ON 

PLANTS  OF  THE  SAME  SPECIES. 


INTKODUCTION. 

THE  subject  of  the  present  volume,  namely  the  dif- 
ferently formed  flowers  normally  produced  by  certain 
kinds  of  plants,  either  on  the  same  stock  or  on  distinct 
stocks,  ought  to  have  been  treated  by  a  professed  botan- 
ist, to  which  distinction  I  can  lay  no  claim.  As  far  as 
the  sexual  relations  of  flowers  are  concerned,  Linnaeus, 
long  ago  divided  them  into  hermaphrodite,  monoecious, 
dioecious,  and  polygamous  species.  This  fundamental 
distinction,  with  the  aid  of  several  subdivisions  in  each 
of  the  four  classes,  will  serve  my  purpose;  but  the  classi- 
fication is  artificial,  and  the  groups  often  pass  into  one 
another. 

The  hermaphrodite  class  contains  two  interesting 
sub-groups,  namely,  heterostyled  and  cleistogamic 
plants;  but  here  are  several  other  less  important 
subdivisions,  presently  to  be  given,  in  which  flowers 
differing  in  various  ways  from  one  another  are  produced 
by  the  same  species. 

Some  plants  were  described  by  me  several  years  ago, 
in  a  series  of  papers  read  before  the  Linnean  Society,* 


*  "  On  the  Two  Forms,  or  Di-      of  Primula,  and  on  their  remark- 
morphic  Condition  in  the  Species      able  Sexual  Eelations."   '  Journal 

1 


2  INTRODUCTION. 

the  individuals  of  which  exist  under  two  or  three 
forms,  differing  in  the  length  of  their  pistils  and 
stamens  and  in  other  respects.  They  were  called  by 
me  dimorphic  and  trimorphic,  but  have  since  been 
better  named  by  Hildebrand,  heterostyled.*  As  I 
have  many  still  unpublished  observations  with  respect 
to  these  plants,  it  has  seemed  to  me  advisable  to  re- 
publish  my  former  papers  in  a  connected  and  cor- 
rected form,  together  with  the  new  matter.  It  will  be 
shown  that  these  heterostyled  plants  are  adapted  for 
reciprocal  fertilisation;  so  that  the  two  or  three  forms, 
though  all  are  hermaphrodites,  are  related  to  one  an- 
other almost  like  the  males  and  females  of  ordinary 
unisexual  animals.  I  will  also  give  a  full  abstract  of 
such  observations  as  have  been  published  since  the  ap- 
pearance of  my  papers;  but  only  those  cases  will  be 
noticed,  with  respect  to  which  the  evidence  seems  fairly 
satisfactory.  Some  plants  have  been  supposed  to  be 
heterostyled  merely  from  their  pistils  and  stamens 
varying  greatly  in  length,  and  I  have  been  myself 
more  than  once  thus  deceived.  With  some  species  the 
pistil  continues  growing  for  a  long  time,  so  that  if  old 
and  young  flowers  are  compared  they  might  be  thought 


of  the  Proceedings  of  the  Linnean  P.     elatior,     Jacq. ;    and    on    the 

Society,'  vol.  vi.  1862,  p.  77.  Hybrid   Nature   of   the   Common 

"On    the    Existence    of    Two  Oxlip.     With  Supplementary  Re- 

Forms,  and  on  their  Reciprocal  marks  on  Naturally  Produced  Hy- 

Sexual  Relation,  in  Several  Species  hrids  in  the  Genus  Verbascum." 

of  the  Genus  Linum."     Ibid.  vol.  Ibid.  vol.  x.  1868,  p.  437. 
vii   1863,  p.  6fl.  *  The  term  "  heterostyled  "  does 

On  the  Sexual    Relations  of  not  express  all  the  differences  be- 

the  Three  Forms  of  Lythrum  sali-  tween  the  forms  ;    but  this  is  a 

caria."    Ibid.  vol.  iii.  1864.  p.  169.  failure  common  in    many  cases. 

On  the  Character  and  Hybrid-  As  the  term  has  been  adopted  by 

like  Nature  of  the  Offspring  from  writers  in  various  countries,  I  am 

the  Illegitimate  Unions  of  Dimor-  unwilling  to  change  it  for  that  of 

phic    and    Tnmorphic    Plants."  lieterogone  or  heteroqonous,  though 

"  AV    «*'  1C868'  &  393'  this  has  been  Pr°P°sed  by  so  high 

s    bpecinc    Differences  an  authority  as  Prof.  Asa  Gray  • 

between  Primula  verts,  Brit.    Fl.  see    the    'American    Naturalist,' 

( var.  offinnalM,  Linn.),  P.  vnlgari*,  Jan.  1877,  p.  42. 
Brit.  Fl.  (var.  acaulis,  Linn.),  and 


INTRODUCTION.  3 

to  be  heterostyled.  Again,  a  species  tending  to  become 
dioacious,  with  the  stamens  reduced  in  some  individuals 
and  with  the  pistils  in  others,  often  presents  a  decep- 
tive appearance.  Unless  it  be  proved  that  one  form 
is  fully  fertile  only  when  it  is  fertilised  with  pollen 
from  another  form,  we  have  not  complete  evidence 
that  the  species  is  heterostyled.  But  when  the  pistils 
and  stamens  differ  in  length  in  two  or  three  sets  of  in- 
dividuals, and  this  is  accompanied  by  a  difference  in 
'the  size  of  the  pollen-grains  or  in  the  state  of  the 
stigma,  we  may  infer  with  much  safety  that  the  species 
is  heterostyled.  I  have,  however,  occasionally  trusted 
to  a  difference  between  the  two  forms  in  the  length 
of  the  pistil  alone,  or  in  the  length  of  the  stigma 
together  with  its  more  or  less  papillose  condition;  and 
in  one  instance  differences  of  this  kind  have  been 
proved  by  trials  made  on  the  fertility  of  the  two  forms, 
to  be  sufficient  evidence. 

The  second  sub-group,  above  referred  to,  consists  of 
hermaphrodite  plants,  which  bear  two  kinds  of  flowers 
— the  one  perfect  and  fully  expanded — the  other  mi- 
nute, completely  closed,  with  the  petals  rudimentary, 
often  with  some  of  the  anthers  aborted,  and  the  re- 
maining ones  together  with  the  stigmas  much  reduced 
in  size;  yet  these  flowers  are  perfectly  fertile.  They 
have  been  called  by  Dr.  Kuhn  *  cleistogamic,  and  they 
will  be  described  in  the  last  chapter  of  this  volume. 
They  are  manifestly  adapted  for  self -fertilisation,  which 


*  'Botanische    Zeitung,'    1867,  partakes  of  the  nature  of  a  mon- 

p.  65.    Several  plants  are  known  strosity.    All  the  flowers  on  the 

occasionally    to    produce    flowers  same  plant  are  commonly  affected 

destitute  of  a  corolla  ;   but  they  in  the  same  manner.     Such  cases, 

belong    to   a     different    class    of  though  they  have  sometimes  been 

cases  from    cleistogamic    flowers,  ranked   as    cleistogamic,    do   not 

This    deficiency  seems    to  result  come  within  our  present  scope  : 

from  the  conditions  to  which  the  see  Dr.  Maxwell  Masters,  '  Vege- 

plants  have  been  subjected,  and  table  Teratology,'  1869,  p.  403. 


4  INTRODUCTION. 

is  effected  at  the  cost  of  a  wonderfully  small  expendi- 
ture of  pollen;  whilst  the  perfect  flowers  produced  by 
the  same  plant  are  capable  of  cross-fertilisation.  Cer- 
tain aquatic  species,  when  they  flower  beneath  the 
water,  keep  their  corollas  closed,  apparently  to  protect 
their  pollen;  they  might  therefore  be  called  cleisto- 
gamic,  but  for  reasons  assigned  in  the  proper  place  are 
not  included  in  the  present  sub-group.  Several  cleis- 
togamic  species,  as  we  shall  hereafter  see,  bury  their 
ovaries  or  young  capsules  in  the  ground.  Some  few 
plants  produce  subterranean  flowers,  as  well  as  ordinary 
ones;  and  these  might  have  been  formed  into  a  small 
separate  subdivision. 

Another  interesting  subdivision  consists  of  certain 
plants,  discovered  by  H.  Miiller,  some  individuals 
of  which  bear  conspicuous  flowers  adapted  for  cross- 
fertilisation  by  the  aid  of  insects,  and  others  much 
smaller  and  less  conspicuous  flowers,  which  have  often 
been  slightly  modified  so  as  to  ensure  self-fertilisation. 
Lysimachia  vulgaris,  Euphrasia  officinalis,  Rhinan- 
thus  crista-galli,  and  Viola  tricolor  come  under  this 
head.*  The  smaller  and  less  conspicuous  flowers  are 
not  closed,  but  as  far  as  the  purpose  which  they  serve 
is  concerned,  namely,  the  assured  propagation  of  the 
species,  they  approach  in  nature  cleistogamic  flowers; 
but  they  differ  from  them  by  the  two  kinds  being  pro- 
duced on  distinct  plants. 

With  many  plants,  the  flowers  towards  the  outside  of 
the  inflorescence  are  much  larger  and  more  conspicu- 
ous than  the  central  ones.  As  I  shall  not  have  occa- 
sion to  refer  to  plants  of  this  kind  in  the  following 
chapters,  I  will  here  give  a  few  details  respecting  them. 


der 


INTRODUCTION.  5 

It  is  familiar  to  every  one  that  the  ray-florets  of  the 
Composites  often  differ  remarkably  from  the  others;  and 
so  it  is  with  the  outer  flowers  of  many  Umbelliferag, 
some  Cruciferae,  and  a  few  other  families.  Several 
species  of  Hydrangea  and  Viburnum  offer  striking 
instances  of  the  same  fact.  The  Eubiaceous  genus 
Mussasnda  presents  a  very  curious  appearance  from  some 
of  the  flowers  having  the  tip  of  one  of  the  sepals 
developed  into  a  large  petal-like  expansion,  coloured 
either  white  or  purple.  The  outer  flowers  in  several 
Acantaceous  genera  are  large  and  conspicuous,  but 
sterile;  the  next  in  order  are  smaller,  open,  moderately 
fertile  and  capable  of  cross-fertilisation;  whilst  the 
central  ones  are  cleistogamic,  being  still  smaller,  closed 
and  highly  fertile;  so  that  here  the  inflorescence  con- 
sists of  three  kinds  of  flowers.*  From  what  we  know 
in  other  cases  of  the  use  of  the  corolla,  coloured  bractere, 
&c.,  and  from  what  H.  Miiller  has  observed  f  on  the 
frequency  of  the  visits  of  insects  to  the  flower-heads  of 
the  Umbelliferse  and  Composites  being  largely  deter- 
mined by  their  conspicuousness,  there  can  be  no  doubt 
that  the  increased  size  of  the  corolla  of  the  outer 
flowers,  the  inner  ones  being  in  all  the  above  cases 
small,  serves  to  attract  insects.  The  result  is  that  cross- 
fertilisation  is  thus  favoured.  Most  flowers  wither 
soon  after  being  fertilised,  but  Hildebrand  states  J  that 
the  ray-florets  of  the  Composite  last  for  a  long  time, 
until  all  those  on  the  disc  are  impregnated;  and  this 
clearly  shows  the  use  of  the  former.  The  ray-florets, 
however,  are  of  service  in  another  and  very  different 
manner,  namely,  by  folding  inwards  at  night  and  dur- 


*  J.  Scott,  '  Journal  of  Botany,'  J  See    his    interesting  memoir, 

London,  new  series,  vol.  i.  1872,  '  Ueber    die    Geschlechtsverhiilt- 

pp.  161-164.  nisse  bei  den  Compositen,'  1869, 

t  '  Die    Befrucbtung    der    Blu-  p.  92. 
men,'  pp.  108,  412. 


6  INTRODUCTION. 

ing  cold  rainy  weather,  so  as  to  protect  the  florets  of 
the  disc.*  Moreover  they  often  contain  matter  which 
is  excessively  poisonous  to  insects,  as  may  be  seen  in 
the  use  of  flea-powder,  and  in  the  case  of  Pyrethrum, 
M.  Belhomme  has  shown  that  the  ray-florets  are  more 
poisonous  than  the  disc-florets  in  the  ratio  of  about  three 
to  two.  "We  may  therefore  believe  that  the  ray-florets 
are  useful  in  protecting  the  flowers  from  being  gnawed 
by  insects,  f 

It  is  a  well-known  yet  remarkable  fact  that  the  cir- 
cumferential flowers  of  many  of  the  foregoing  plants 
have  both  their  male  and  female  reproductive  organs 
aborted,  as  with  the  Hydrangea,  Viburnum,  and  certain 
Compositae;  or  the  male  organs  alone  are  aborted,  as 
in  many  Compositae.  Between  the  sexless,  female,  and 
hermaphrodite  states  of  these  latter  flowers,  the  finest 
gradations  may  be  traced,  as  Hildebrand  has  shown.J 
He  also  shows  that  there  is  a  close  relation  between 
the  size  of  the  corolla  in  the  ray-florets  and  the  degree 
of  abortion  in  their  reproductive  organs.  As  we  have 
good  reason  to  believe  that  these  florets  are  highly 
serviceable  to  the  plants  which  possess  them,  more 
especially  by  rendering  the  flower-heads  conspicuous 
to  insects,  it  is  a  natural  inference  that  their  corollas 
have  been  increased  in  size  for  this  special  purpose; 
and  that  their  development  has  subsequently  led, 


*  Kerner  clearly  shows  that  this  and  thus  the  organs  of  fructifica- 
is  the  case  :  '  Die  Schutzmittel  des  tion  are  protected.  My  grand- 
Pollens,' 1873,  p.  28.  father,  in  1790  ('Loves  of  the 

t  '  Gardener's  Chronicle,'  1861,  Plants,'  canto  iii.  note  to  lines  184, 

p.     1067.        Lindley,     'Vegetable  188),  remarks  that  "The  flowers 

Kingdom.'    on    Chrysanthemum,  or  petals  of  plants  are  perhaps  in 

1853,  p.  706.     Kerner  in  his  inter-  general    more    acrid    than    their 

esting   essay  ( '  Die    Schutzmittel  leaves  ;  hence  they  are  much  sel- 

der    Bliithen    gegen    unherufene  domer  eaten  hy  insects." 

Gaste,' 1875,  p.  19)  insists  that  the  |    'TJeber    die    Geschlechtsver- 

petals  of  most  plants  contain  mat-  haltnisse    hei    den    Compositen,' 

ter  which  is  offensive  to  insects,  1869,  pp.  78-91. 
BO  that  they  are  seldom  gnawed, 


INTRODUCTION.  ? 

through  the  principle  of  compensation  or  balance- 
ment,  to  the  more  or  less  complete  reduction  of  the 
reproductive  organs.  But  an  opposite  view  may  be 
maintained,  namely,  that  the  reproductive  organs 
first  began  to  fail,  as  often  happens  under  cultiva- 
tion,* and,  as  a  consequence,  the  corolla  became, 
through  compensation,  more  highly  developed.  This 
view,  however,  is  not  probable,  for  when  hermaphrodite 
plants  become  dioecious  or  gyno-dicecious — that  is, 
are  converted  into  hermaphrodites  and  females — the 
corolla  of  the  female  seems  to  be  almost  invariably 
reduced  in  size  in  consequence  of  the  abortion  of  the 
male  organs.  The  difference  in  the  result  in  these  two 
classes  of  cases  may  perhaps  be  accounted  for  by  the 
matter  saved  through  the  abortion  of  the  male  organs  in 
the  females  of  gyno-dicecious  and  dioecious  plants  being 
directed  (as  we  shall  see  in  a  future  chapter)  to  the  for- 
mation of  an  increased  supply  of  seeds;  whilst  in  the 
case  of  the  exterior  florets  and  flowers  of  the  plants 
which  we  are  here  considering,  such  matter  is  expended 
in  the  development  of  a  conspicuous  corolla.  Whether 
in  the  present  class  of  cases  the  corolla  was  first  affected, 
as  seems  to  me  the  more  probable  view,  or  the  reproduc- 
tive organs  first  failed,  their  states  of  development  are 
now  firmly  correlated.  We  see  this  well  illustrated  in 
Hydrangea  and  Viburnum;  for  when  these  plants  are 
cultivated,  the  corollas  of  both  the  interior  and  exterior 
flowers  become  largely  developed,  and  their  reproductive 
organs  are  aborted. 

There  is  a  closely  analogous  subdivision  of  plants, 
including  the  genus  Muscari  (or  Feather  Hyacinth) 
and  the  allied  Bellevalia,  which  bear  both  perfect 


*  I  have  discussed  this  subject  in    xviii.   2nd  edit.  vol.   ii.  pp.  152, 
my   'Variation    of   Animals  and     156. 
Plants  under  Domestication,'  chap. 


g  INTRODUCTION. 

flowers  and  closed  bud-like  bodies  that  never  expand. 
The  latter  resemble  in  this  respect  cleistogamic 
flowers,  but  differ  widely  from  them  in  being  sterile 
and  conspicuous.  Not  only  the  aborted  flower-buds 
and  their  peduncles  (which  are  elongated  apparently 
through  the  principle  of  compensation)  are  brightly 
coloured,  but  so  is  the  upper  part  of  the  spike — 
all,  no  doubt,  for  the  sake  of  guiding  insects  to  the 
inconspicuous  perfect  flowers.  From  such  cases  as 
these  we  may  pass  on  to  certain  Labiatse,  for  instance, 
Salvia  Horminum,  in  which  (as  I  hear  from  Mr.  Thisel- 
ton  Dyer)  the  upper  bracts  are  enlarged  and  brightly 
coloured,  no  doubt  for  the  same  purpose  as  before,  with 
the  flowers  suppressed. 

In  the  Carrot  and  some  allied  TJmbelliferaB,  the  cen- 
tral flower  has  its  petals  somewhat  enlarged,  and  these 
are  of  a  dark  purplish-red  tint;  but  it  cannot  be  sup- 
posed that  this  one  small  flower  makes  the  large  white 
umbel  at  all  more  conspicuous  to  insects.  The  central 
flowers  are  said  *  to  be  neuter  or  sterile,  but  I  ob- 
tained by  artificial  fertilisation  a  seed  (fruit)  appa- 
rently perfect  from  one  such  flower.  Occasionally  two 
or  three  of  the  flowers  next  to  the  central  one  are  simi- 
larly characterised;  and  according  to  Vaucher  f  "  cette 
singuliere  degeneration  s'etend  quelquefois  a  I'ombelle 
entiere."  That  the  modified  central  flower  is  of  no 
functional  importance  to  the  plant  is  almost  certain. 
It  may  perhaps  be  a  remnant  of  a  former  and  ancient 
condition  of  the  species,  when  one  flower  alone,  the 
central  one,  was  female  and  yielded  seeds,  as  in  the 
umbelliferous  genus  Echinophora.  There  is  nothing 
surprising  in  the  central  flower  tending  to  retain  its 


•'The   English  Flora,'  by  Sir    rope,' 1841,  torn.  ii.  p.  614.    On  the 
J.  E  Smith,  1824,  vol.  ii.  p.  39.          Echinophora,  p.  627. 
t  '  Hist.  Phys.  des  Plantes  d'Eu- 


INTRODUCTION.  9 

former  condition  longer  than  the  others;  for  when  ir- 
regular flowers  become  regular  or  peloric,  they  are  apt 
to  be  central;  and  such  peloric  flowers  apparently  owe 
their  origin  either  to  arrested  development — that  is,  to 
the  preservation  of  an  early  stage  of  development — or 
to  reversion.  Central  and  perfectly  developed  flowers 
in  not  a  few  plants  in  the  normal  condition  (for  in- 
stance, the  common  Eue  and  Adoxa)  differ  slightly  in 
structure,  as  in  the  number  of  the  parts,  from  the  other 
flowers  on  the  same  plant.  All  such  cases  seem  con- 
nected with  the  fact  of  the  bud  which  stands  at  the 
end  of  the  shoot  being  better  nourished  than  the  others, 
as  it  receives  the  most  sap.* 

The  cases  hitherto  mentioned  relate  to  hermaphro- 
dite species  which  bear  differently  constructed  flowers; 
but  there  are  some  plants  that  produce  differently 
formed  seeds,  of  which  Dr.  Kuhn  has  given  a  list.f 
With  the  Umbelliferse  and  Composite,  the  flowers  that 
produce  these  seeds  likewise  differ,  and  the  differences 
in  the  structure  of  the  seeds  are  of  a  very  important 
nature.  The  causes  which  have  led  to  differences  in  the 
seeds  on  the  same  plant  are  not  known;  and  it  is  very 
doubtful  whether  they  subserve  any  special  end. 

We  now  come  to  our  second  Class,  that  of  monoecious 
species,  or  those  which  have  their  sexes  separated  but 
borne  on  the  same  plant.  The  flowers  necessarily 
differ,  but  when  those  of  one  sex  include  rudiments 
of  the  other  sex,  the  difference  between  the  two  kinds 
is  usually  not  great.  When  the  difference  is  great, 
as  we  see  in  catkin-bearing  plants,  this  depends 


*  This  whole  subject,  including    mesti cation,' chap.  xxvi.  2nd  edit, 
pelorism,  has  been  discussed,  and    vol.  ii.  p.  338. 
references  given,  in  my  '  Variation        f  '  Bot.  Zeitung,'  1867,  p.  67. 
of  Animals  and  Plants  under  Do- 
3 


10 


INTRODUCTION. 


largely  on  many  of  the  species  in  this,  as  well  as  in 
the  next  or  dioecious  class,  being  fertilised  by  the 
aid  of  the  wind;  *  for  the  male  flowers  have  in  this 
case  to  produce  a  surprising  amount  of  incoherent 
pollen.  Some  few  monoecious  plants  consist  of  two 
bodies  of  individuals,  with  their  flowers  differing  in 
function,  though  not  in  structure;  for  certain  indivi- 
duals mature  their  pollen  before  the  female  flowers  on 
the  same  plant  are  ready  for  fertilisation,  and  are  called 
proterandrous ;  whilst  conversely  other  individuals, 
called  proterogynous,  have  their  stigmas  mature  before 
their  pollen  is  ready.  The  purpose  of  this  curious  func- 
tional difference  obviously  is  to  favour  the  cross-fertili- 
sation of  distinct  plants.  A  case  of  this  kind  was  first 
observed  by  Delpino  in  the  Walnut  (Juglans  regia),  and 
has  since  been  observed  with  the  common  Nut  (Corylus 
avellana).  According  to  H.  Miiller,  the  individual 
plants  of  a  few  hermaphrodite  species  differ  in  a  like 
manner;  some  being  proterandrous  and  others  pro- 
terogynous. f  On  cultivated  trees  of  the  Walnut  and 
Mulberry,  the  male  flowers  have  been  observed  to  abort 
on  certain  individuals,^  which  have  thus  been  converted 
into  females;  but  whether  there  are  any  species  in  a 
state  of  nature  which  co-exist  as  monoecious  and  female 
individuals,  I  do  not  know. 

The  third  Class  consists  of  dioscious  species,  and  the 
remarks  made  under  the  last  class  with  respect  to  the 
amount  of  difference  between  the  male  and  female 
flowers  are  here  applicable.  It  is  at  present  an  inex- 


*  Delpino,  'Studi  sopra  uno  xi.  p.  507,  and  1875,  p.  26.  On 

iKiiaggio  Anemofilo,'  Firenze,  proterandrous  and  proterogynous 
hermaphrodite  individuals  of  the 

t  Delpino,  Ult.  Osservazioni  same  species,  see  H.  Miiller,  '  Die 

Bul1*  ^P"1,?/  part-  iL  fasc-  "•  Befruchtunu,'  &c.,  pp.  285,  339. 

&-n            n  Wotterhan  and    H.  J  '  Gardener's  Chron.,'  1847,  pp. 

Muller  on  Corylus,  '  Nature,'  vol.  541  558 


INTRODUCTION.  11 

plicable  fact  that  with  some  dioecious  plants,  of  which 
the  Eestiaceae  of  Australia  and  the  Cape  of  Good  Hope 
offer  the  most  striking  instance,  the  differentiation  of 
the  sexes  has  affected  the  whole  plant  to  such  an  extent 
(as  I  hear  from  Mr.  Thiselton  Dyer)  that  Mr.  Bentham 
and  Professor  Oliver  have  often  found  it  impossible  to 
match  the  male  and  female  specimens  of  the  same  spe- 
cies. In  my  seventh  chapter  some  observations  will  be 
given  on  the  gradual  conversion  of  heterostyled  and  of 
ordinary  hermaphrodite  plants  into  dioecious  or  sub- 
dio2eious  species. 

The  fourth  and  last  Class  consists  of  the  plants  which 
were  called  polygamous  by  Linmeus;  but  it  appears  to 
me  that  it  would  be  convenient  to  confine  this  term  to 
the  species  which  co-exist  as  hermaprodites,  males,  and 
females;  and  to  give  new  names  to  several  other  com- 
binations of  the  sexes — a  plan  which  I  shall  here 
follow.  Polygamous  plants,  in  this  confined  sense  of 
the  term,  may  be  divided  into  two  sub-groups,  accord- 
ing as  the  three  sexual  forms  are  found  on  the  same 
individual  or  on  distinct  individuals.  Of  this  latter 
or  trioicous  sub-group,  the  common  Ash  (Fraxinus  ex- 
celsior) offers  a  good  instance:  thus,  I  examined  during 
the  spring  and  autumn  fifteen  trees  growing  in  the 
same  field;  and  of  these,  eight  produced  male  flowers 
alone,  and  in  the  autumn  not  a  single  seed;  four  pro- 
duced only  female  flowers,  which  set  an  abundance  of 
seeds;  three  were  hermaphrodites,  which  had  a  dif- 
ferent aspect  from  the  other  trees  whilst  in  flower,  and 
two  of  them  produced  nearly  as  many  seeds  as  the  fe- 
male trees,  whilst  the  third  produced  none,  so  that  it 
was  in  function  a  male.  The  separation  of  the  sexes, 
however,  is  not  complete  in  the  Ash;  for  the  female 
flowers  include  stamens,  which  drop  off  at  an  early 


12  INTRODUCTION. 

period,  and  their  anthers,  which  never  open  or  dehisce, 
generally  contain  pulpy  matter  instead  of  pollen.  On 
some  female  trees,  however,  I  found  a  few  anthers  con- 
taining pollen-grains  apparently  sound.  On  the  male 
trees  most  of  the  flowers  include  pistils,  but  these  like- 
wise drop  off  at  an  early  period;  and  the  ovules,  which 
ultimately  abort,  are  very  small  compared  with  those 
in  female  flowers  of  the  same  age. 

Of  the  other  or  monoecious  sub-group  of  polygamous 
plants,  or  those  which  bear  hermaphrodite,  male,  and 
female  flowers  on  the  same  individual,  the  common 
Maple  (Acer  campestre)  offers  a  good  instance;  but  Lecoq 
states  *  that  some  trees  are  truly  dioecious,  and  this 
shows  how  easily  one  state  passes  into  another. 

A  considerable  number  of  plants  generally  ranked 
as  polygamous  exist  under  only  two  forms,  namely,  as 
hermaphrodites  and  females;  and  these  may  be  called 
gyno-dicecious,  of  which  the  common  Thyme  offers  a 
good  example.  In  my  seventh  chapter  I  shall  give 
some  observations  on  plants  of  this  nature.  Other  spe- 
cies, for  instance  several  kinds  of  Atriplex,  bear  on  the 
same  plant  hermaphrodite  and  female  flowers;  and  these 
might  be  called  gyno-moncecious,  if  a  name  were  desira- 
ble for  them. 

Again  there  are  plants  which  produce  hermaphro- 
dite and  male  flowers  on  the  same  individual,  for  in- 
stance, some  species  of  Galium,  Veratrum,  &c.;  and 
these  might  be  called  andro-moncecious.  If  there 
exist  plants,  the  individuals  of  which  consist  of  herma- 
phrodites and  males,  these  might  be  distinguished 
as  andro-dicecious.  But,  after  making  inquiries  from 
several  botanists,  I  can  hear  of  no  such  cases.  Lecoq, 
however,  states, f  but  without  entering  into  full  details, 


*  '  Geographic  Botanique,'  torn.  v.  p.  367.        f  Ibid.  torn.  iv.  p.  488. 


INTRODUCTION.  13 

that  some  plants  of  Caltha  palustris  produce  only  male 
flowers,  and  that  these  live  mingled  with  the  her- 
maphrodites. The  rarity  of  such  cases  as  this  last  one 
is  remarkable,  as  the  presence  of  hermaphrodite  and 
male  flowers  on  the  same  individual  is  not  an  un- 
usual occurrence;  it  would  appear  as  if  Nature  did 
not  think  it  worth  while  to  devote  a  distinct  indi- 
vidual to  the  production  of  pollen,  excepting  when 
this  was  indispensably  necessary,  as  in  the  case  of 
dioecious  species. 

I  have  now  finished  my  brief  sketch  of  the  several 
cases,  as  far  as  known  to  me,  in  which  flowers  differing 
in  structure  or  in  function  are  produced  by  the  same 
species  of  plant.  Full  details  will  be  given  in  the  fol- 
lowing chapters  with  respect  to  many  of  these  plants. 
I  will  begin  with  the  heterostyled,  then  pass  on  to  cer- 
tain dioecious,  sub-dioscious,  and  polygamous  species, 
and  end  with  the  cleistogamic.  For  the  convenience  of 
the  reader,  and  to  save  space,  the  less  important  cases 
and  details  have  been  printed  in  smaller  type. 

I  cannot  close  this  Introduction  without  expressing 
my  warm  thanks  to  Dr.  Hooker  for  supplying  me  with 
specimens  and  for  other  aid;  and  to  Mr.  Thiselton  Dyer 
and  Professor  Oliver  for  giving  me  much  information 
and  other  assistance.  Professor  Asa  Gray,  also,  has  uni- 
formly aided  me  in  many  ways.  To  Fritz  Miiller  of  St. 
Catharina,  in  Brazil,  I  am  indebted  for  many  dried 
flowers  of  heterostyled  plants,  often  accompanied  with 
valuable  notes. 


14        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAT.  I. 


CHAPTER  I. 
HETEBOSTYLED  DIMOEPHIC  PLANTS:  PKIMULACILE. 

Primula  veris  or  the  Cowslip — Differences  in  structure  between  the 
two  forms — Their  degrees  of  fertility  when  legitimately  and  illegit- 
imately united — P.  elatior,  vulgaris,  Sinensis,  auricula,  &c. — Sum- 
mary on  the  fertility  of  the  heterostyled  species  of  Primula — 
Homostyled  species  of  Primula — Hottonia  palustris — Androsace 
Vitalliana. 

IT  has  long  been  known  to  botanists  that  the  com- 
mon Cowslip  (Primula  veris,  Brit.  Flora,  var.  officinalis, 
Lin.)  exists  under  two  forms,  about  equally  numerous, 
which  obviously  differ  from  each  other  in  the  length 
of  their  pistils  and  stamens.*  This  difference  has 
hitherto  been  looked  at  as  a  case  of  mere  varia- 
bility, but  this  view,  as  we  shall  presently  see,  is  far 
from  the  true  one.  Florists  who  cultivate  the  Polyan- 
thus and  Auricula  have  long  been  aware  of  the  two 
kinds  of  flowers,  and  they  call  the  plants  which  dis- 
play the  globular  stigma  at  the  mouth  of  the  corolla, 
"  pin-headed  "  or  "  pin-eyed,"  and  those  which  display 
the  anthers,  "thrum-eyed/'  f  I  will  designate. the  two 
forms  as  the  long-styled  and  short-styled. 

The  pistil  in  the  long-styled  form  is  almost  exactly 
twice  as  long  as  that  of  the  short-styled.  The  stigma 


*  This  fact,  according  to  von  that  some  weaver  who  cultivated 

Mohl(  Bot.  Zeitung,'1863,p.326),  the  polyanthus  invented  this 

was  first  observed  by  Persoon  in  name,  from  being  struck  with 

the  year  1794.  some  degree  of  resemblance  be- 

Tln  Johnson's  Dictionary,  tween  the  cluster  of  anthers  in  the 

thrum  is  said  to  be  the  ends  of  mouth  of  the  coroUa  and  the  ends 

weavers'  threads ;  and  I  suppose  of  his  threads. 


CHAP.  I.  PEIMULA  VERIS.  15 

stands  in  the  mouth  of  the  corolla,  or  projects  just 
above  it,  and  is  thus  externally  visible.  It  stands 
high  above  the  anthers,  which  are  situated  halfway 
down  the  tube  and  cannot  be  easily  seen.  In  the 
short-styled  form  the  anthers  are  attached  near  the 
mouth  of  the  tube,  and  therefore  stand  above  the 
stigma,  which  is  seated  in  about  the  middle  of  the 
tubular  corolla.  The  corolla  itself  is  of  a  different 

Fig.  1. 


Long-styled  form.       Short-styled  form. 
PRIMULA  VEEIS. 

shape  in  the  two  forms;  the  throat  or  expanded 
portion  above  the  attachment  of  the  anthers  being 
much  longer  in  the  long-styled  than  in  the  short- 
styled  form.  Village  children  notice  this  difference, 
as  they  can  best  make  necklaces  by  threading  and 
slipping  the  corollas  of  the  long-styled  flowers  into 
one  another.  But  there  are  much  more  important 
differences.  The  stigma  in  the  long-styled  form 


16        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

is  globular;  in  the  short-styled  it  is  depressed  on 
the  summit,  so  that  the  longitudinal  axis  of  the 
former  is  sometimes  nearly  double  that  of  the  latter. 
Although  it  is  somewhat  variable  in  shape,  one  differ- 
ence is  persistent,  namely,  roughness:  in  some  speci- 
mens carefully  compared,  the  papillae  which  render 
the  stigma  rough  were  in  the  long-styled  form  from 
twice  to  thrice  as  long  as  in  the  short-styled.  The 
anthers  do  not  differ  in  size  in  the  two  forms,  which 
I  mention,  because  this  is  the  case  with  some  hetero- 
styled  plants.  The  most  remarkable  difference  is  in 
the  pollen-grains.  I  measured  with  the  micrometer 
many  specimens,  both  dry  and  wet,  taken  from  plants 
growing  in  different  situations,  and  always  found  a 
palpable  difference.  The  grains  distended  with  water 
from  the  short-styled  flowers  were  about  .038  mm. 
(4rTiV  of  an  incn)  in  diameter,  whilst  those  from  the 
long-styled  were  about  .0254  mm.  (T15Vjr  of  an  inch), 
which  is  in  the  ratio  of  100  to  67.  The  pollen-grains, 
therefore,  from  the  longer  stamens  of  the  short-styled 
form  are  plainly  larger  than  those  from  the  shorter 
stamens  of  the  long-styled.  When  examined  dry, 
the  smaller  grains  are  seen  under  a  low  power  to 
be  more  transparent  than  the  larger  grains,  and 
apparently  in  a  greater  degree  than  can  be  ac- 
counted for  by  their  less  diameter.  There  is  also  a 
difference  in  shape,  the  grains  from  the  short-styled 
plants  being  nearly  spherical,  those  from  the  long- 
styled  being  oblong  with  the  angles  rounded;  this 
difference  disappears  when  the  grains  are  distended 
with  water.  The  long-styled  plants  generally  tend 
to  flower  a  little  before  the  short-styled;  for  instance, 
I  had  twelve  plants  of  each  form  growing  in  separate 
pots  and  treated  in  every  respect  alike;  and  at  the 
time  when  only  a  single  short-styled  plant  was  in 


CHAP.  I.  PRIMULA  VERIS.  1Y 

flower,  seven  of  the  long-styled  had  expanded  their 
flowers. 

We  shall,  also,  presently  see  that  the  short-styled 
plants  produce  more  seed  than  the  long-styled.  It  is 
remarkable,  according  to  Professor  Oliver,*  that  the 
ovules  in  the  unexpanded  and  unimpregnated  flowers  of 
the  latter  are  considerably  larger  than  those  of  the  short- 
styled  flowers;  and  this  I  suppose  is  connected  with  the 
long-styled  flowers  producing  fewer  seeds,  so  that  the 
ovules  have  more  space  and  nourishment  for  rapid  de- 
velopment. 

To  sum  up  the  difference: — The  long-styled  plants 
have  a  much  longer  pistil,  with  a  globular  and  much 
rougher  stigma,  standing  high  above  the  anthers.  The 
stamens  are  short;  the  grains  of  pollen  smaller  and  ob- 
long in  shape.  The  upper  half  of  the  tube  of  the 
corolla  is  more  expanded.  The  number  of  seeds  pro- 
duced is  smaller  and  the  ovules  larger.  The  plants 
tend  to  flower  first. 

The  short-styled  plants  have  a  short  pistil,  half  the 
length  of  the  tube  of  the  corolla,  with  a  smooth  de- 
pressed stigma  standing  beneath  the  anthers.  The  sta- 
mens are  long;  the  grains  of  pollen  are  spherical  and 
larger.  The  tube  of  the  corolla  is  of  uniform  diameter 
except  close  to  the  upper  end.  The  number  of  seeds 
produced  is  larger. 

I  have  examined  a  large  number  of  flowers;  and 
though  the  shape  of  the  stigma  and  the  length  of  the 
pistil  both  vary,  especially  in  the  short-styled  form,  I 
have  never  met  with  any  transitional  states  between 
the  two  forms  in  plants  growing  in  a  state  of  nature. 
There  is  never  the  slightest  doubt  under  which  form  a 
plant  ought  to  be  classed.  The  two  kinds  of  flowers  are 


*  'Nat.  Hist.  Review,'  July,  1862,  p.  237. 


18        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

never  found  on  the  same  individual  plant.  I  marked 
many  Cowslips  and  Primroses,  and  on  the  following 
year  all  retained  the  same  character,  as  did  some  in  my 
garden  which  flowered  out  of  their  proper  season  in  the 
autumn.  Mr.  W.  Wooler,  of  Darlington,  however,  in- 
forms us  that  he  has  seen  early  blossoms  on  the  Polyan- 
thus,* which  were  not  long-styled,  but  became  so  later 
in  the  season.  Possibly  in  this  case  the  pistils  may  not 
have  been  fully  developed  during  the  early  spring.  An 
excellent  proof  of  the  permanence  of  the  two  forms  may 
be  seen  in  nursery-gardens,  where  choice  varieties  of  the 
Polyanthus  are  propagated  by  division;  and  I  found 
whole  beds  of  several  varieties,  each  consisting  exclu- 
sively of  the  one  or  the  other  form.  The  two  forms  exist 
in  the  wild  state  in  about  equal  numbers:  I  collected 
522  umbels  from  plants  growing  in  several  stations, 
taking  a  single  umbel  from  each  plant;  and  241  were 
long-styled,  and  281  short-styled.  No  difference  in  tint 
or  size  could  be  perceived  in  the  two  great  masses  of 
flowers. 

We  shall  presently  see  that  most  of  the  species  of 
Primula  exist  under  two  analogous  forms;  and  it  may 
be  asked  what  is  the  meaning  of  the  above-described 
important  differences  in  their  structure?  The  ques- 
tion seems  well  worthy  of  careful  investigation,  and 
I  will  give  my  observations  on  the  cowslip  in  detail. 
The  first  idea  which  naturally  occurred  to  me  was, 
that  this  species  was  tending  towards  a  dioecious 
condition;  that  the  long-styled  plants,  with  their 
longer  pistils,  rougher  stigmas,  and  smaller  pollen- 
grains,  were  more  feminine  in  nature,  and  would  pro- 
duce more  seed;— that  the  short-styled  plants,  with 
their  shorter  pistils,  longer  stamens,  and  larger  pol- 


*  I  have   proved  by  numerous    that  the  Polyanthus  is  a  variety 
experiments,  hereafter  to  be  given,     of  Primula  veris. 


CHAP.  I. 


PRIMULA  VERIS. 


19 


len-grains,  were  more  masculine  in  nature.  Accord- 
ingly, in  1860,  I  marked  a  few  cowslips  of  both  forms 
growing  in  my  garden,  and  others  growing  in  an 
open  field,  and  others  in  a  shady  wood,  and  gathered 
and  weighed  the  seed.  In  all  the  lots  the  short- 
styled  plants  yielded,  contrary  to  my  expectation,  most 
seed.  Taking  the  lots  together,  the  following  is  the 
result : — 

TABLE  1. 


— 

Number 

&» 

Number  of 
Umbels 
produced. 

Number  of 
Capsules 
produced. 

Weight  of 
Seed 
In  grains. 

9 

33 

199 

83 

13 

51 

261 

91 

If  we  compare  the  weight  from  an  equal  number  of 
plants,  and  from  an  equal  number  of  umbels,  and  from 
an  equal  number  of  capsules  of  the  two  forms,  we  get 
the  following  results: — 

TABLE  2. 


— 

Number 
of 
Plants. 

Weight 
of  Sled 
Ingrains. 

Number 
of 
Umbel.. 

Seed. 

Number 

tar 

"pail;11 

Short-styled  cowslips      .     . 

10 

92 

100 

251 

100 

41 

Long-styled  cowslips  .     .    . 

10 

70 

100 

178 

100 

34 

So  that,  by  all  these  standards  of  comparison,  the 
short -styled  form  is  the  more  fertile;  if  we  take  the 
number  of  umbels  (which  is  the  fairest  standard,  for 
large  and  small  plants  are  thus  equalised),  the  short- 
styled  plants  produce  more  seed  than  the  long-styled, 
in  the  proportion  of  nearly  four  to  three. 

In  1861  the  trial  was  made  in  a  fuller  and  fairer 
manner.  A  number  of  wild  plants  had  been  trans- 


HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


planted  during  the  previous  autumn  into  a  large  bed 
in  my  garden,  and  all  were  treated  alike;  the  result 
was: — 

TABLE  3. 


— 

Number 
of 

Pliints. 

Number 
of 
Umbels. 

Weight 
of  Seed  in 
(trains. 

Short-styled  cowslips  .    . 

47 

173 

745 

Long-styled  cowslips  .    . 

58 

208 

692 

These  figures  give  us  the  following  proportions: — 
TABLE  4. 


— 

Number 
of 
Plants. 

Te^f 
grain.. 

Number 
UmbeH. 

Weight 
of  Seed  in 
grain.. 

Short-styled  cowslips  
Long-styled  cowslips  

100 
100 

1585 
1093 

100 
100 

430 
332 

The  season  was  much  more  favourable  this  year  than 
the  last;  the  plants  also  now  grew  in  good  soil,  instead 
of  in  a  shady  wood,  or  struggling  with  other  plants  in 
the  open  field;  consequently,  the  actual  produce  of 
seed  was  considerably  larger.  Nevertheless  we  have 
the  same  relative  result;  for  the  short-styled  plants 
produced  more  seed  than  the  long-styled  in  nearly  the 
proportion  of  three  to  two;  but  if  we  take  the  fairest 
standard  of  comparison,  namely,  the  product  of  seeds 
from  an  equal  number  of  umbels,  the  excess  is,  as  in 
the  former  case,  nearly  as  four  to  three. 

Looking  to  these  trials  made  during  two  successive 
years  on  a  large  number  of  plants,  we  may  safely  con- 
clude that  the  short-styled  form  is  more  productive 
than  the  long-styled  form,  and  the  same  result  holds 
good  with  some  other  species  of  Primula.  Consequently 


CHAP.  I. 


PRIMULA  VERIS. 


21 


my  anticipation  that  the  plants  *vith  longer  pistils, 
rougher  stigmas,  shorter  stamens,  and  smaller  pollen- 
grains,  would  prove  to  be  more  feminine  in  nature,  is 
exactly  the  reverse  of  the  truth. 

In  1860  a  few  umbels  on  some  plants  of  both  the 
long-styled  and  short-styled  form,  which  had  been  cov- 
ered by  a  net,  did  not  produce  any  seed,  though  other 
umbels  on  the  same  plants,  artificially  fertilised,  pro- 
duced an  abundance  of  seed;  and  this  fact  shows  that 
the  mere  covering  in  itself  was  not  injurious.  Accord- 
ingly, in  1861,  several  plants  were  similarly  covered 
just  before  they  expanded  their  flowers;  these  turned 
out  as  follows: — 

TABLE  5. 


— 

Number 
of 

Plants. 

Number  of 
Umbeh 
produced. 

Product  of  Seed. 

Short-styled  .... 

6 

24 

f  1.3  grain  weight  of  seed,  or 
1     about  50  in  number. 

Long-styled  .... 

18 

74 

Not  one  seed. 

Judging  from  the  exposed  plants  which  grew  all  round 
in  the  same  bed,  and  had  been  treated  in  the  same 
manner,  excepting  that  they  had  been  exposed  to 
the  visits  of  insects,  the  above  six  short-styled  plants 
ought  to  have  produced  92  grains'  weight  of  seed 
instead  of  only  1.3;  and  the  eighteen  long-styled 
plants,  which  produced  not  one  seed,  ought  to  have 
produced  above  200  grains'  weight.  The  production  of 
a  few  seeds  by  the  short-styled  plants  was  probably  due 
to  the  action  of  Thrips  or  of  some  other  minute  insect. 
It  is  scarcely  necessary  to  give  any  additional  evi- 
dence, but  I  may  add  that  ten  pots  of  polyanthuses  and 
cowslips  of  both  forms,  protected  from  insects  in  my 
greenhouse,  did  not  set  one  pod,  though  artificially  fer- 


22        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

tilised  flowers  in  other  pots  produced  an  abundance. 
We  thus  see  that  the  visits  of  insects  are  absolutely 
necessary  for  the  fertilisation  of  Primula  veris.  If  the 
corolla  of  the  long-styled  form  had  dropped  off,  in- 
stead of  remaining  attached  in  a  withered  state  to 
the  ovarium,  the  anthers  attached  to  the  lower  part  of 
the  tube  with  some  pollen  still  adhering  to  them 
would  have  been  dragged  over  the  stigma,  and  the 
flowers  would  have  been  partially  self-fertilised,  as  is 
the  case  with  Primula  Sinensis  through  this  means. 
It  is  a  rather  curious  fact  that  so  trifling  a  difference 
as  the  falling-off  of  the  withered  corolla  should  make 
a  very  great  difference  in  the  number  of  seeds  pro- 
duced by  a  plant,  if  its  flowers  are  not  visited  by 
insects. 

The  flowers  of  the  cowslip  and  of  the  other  species 
of  the  genus  secrete  plenty  of  nectar;  and  I  have 
often  seen  humble-bees,  especially  B.  hortorum  and  mus- 
corum,  sucking  the  former  in  a  proper  manner,*  though 
they  sometimes  bite  holes  through  the  corolla.  No  doubt 
moths  likewise  visit  the  flowers,  as  one  of  my  sons 
caught  Cucullia  verbasci  in  the  act.  The  pollen  readily 
adheres  to  any  thin  object  which  is  inserted  into  a 
flower.  The  anthers  in  the  one  form  stand  nearly,  but 
not  exactly,  on  a  level  with  the  stigma  of  the  other; 
for  the  distance  between  the  anthers  and  stigma  in  the 
short-styled  form  is  greater  than  that  in  the  long- 
styled,  in  the  ratio  of  100  to  90.  This  difference  is 
the  result  of  the  anthers  in  the  long-styled  form 
standing  rather  higher  in  the  tube  than  does  the 
stigma  in  the  short-styled,  and  this  favours  their 
pollen  being  deposited  on  it.  It  follows  from  the 
position  of  the  organs  that  if  the  proboscis  of  a 


*  H-  Mullor  has  also  seen  Antho-    sucking    the  flowers       'Nature' 
phora  pilipes   and    a    Bombylius    Dec.  10th,  1874,  p.  111. 


CHAP.  I.  PEIMULA  VERIS.  23 

dead  humble-bee,  or  a  thick  bristle  or  rough  needle, 
be  pushed  down  the  corolla,  first  of  one  form  and 
then  of  the  other,  as  an  insect  would  do  in  visiting  the 
two  forms  growing  mingled  together,  pollen  from 
the  long-stamened  form  adheres  round  the  base  of 
the  object,  and  is  left  with  certainty  on  the  stigma 
of  the  long-styled  form;  whilst  pollen  from  the  short 
stamens  of  the  long-styled  form  adheres  a  little  way 
above  the  extremity  of  the  object,  and  some  is 
generally  left  on  the  stigma  of  the  other  form.  In 
accordance  with  this  observation  I  found  that  the 
two  kinds  of  pollen,  which  could  easily  be  recog- 
nised under  the  microscope,  adhered  in  this  manner 
to  the  proboscides  of  the  two  species  of  humble- 
bees  and  of  the  moth,  which  were  caught  visiting 
the  flowers;  but  some  small  grains  were  mingled 
with  the  larger  grains  round  the  base  of  the  proboscis, 
and  conversely  some  large  grains  with  the  small 
grains  near  the  extremity  of  the  proboscis.  Thus 
pollen  will  be  regularly  carried  from  the  one  form 
to  the  other,  and  they  will  reciprocally  fertilise  one 
another.  Nevertheless  an  insect  in  withdrawing  its 
proboscis  from  the  corolla  of  the  long-styled  form 
cannot  fail  occasionally  to  leave  pollen  from  the  same 
flower  on  the  stigma;  and  in  this  case  there  might 
be  self-fertilisation.  But  this  will  be  much  more 
likely  to  occur  with  the  short-styled  form;  for  when  I 
inserted  a  bristle,  or  other  such  objects  in  the  corolla 
of  this  form,  and  had,  therefore,  to  pass  it  down  be- 
tween the  anthers  seated  round  the  mouth  of  the 
corolla,  some  pollen  was  almost  invariably  carried 
down  and  left  on  the  stigma.  Minute  insects,  such 
as  Thrips,  which  sometimes  haunt  the  flowers,  would 
likewise  be  apt  to  cause  the  self -fertilisation  of  both 
forms. 


24        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

The  several  foregoing  facts  led  me  to  try  the  effects 
of  the  two  kinds  of  pollen  on  the  stigmas  of  the 
two  forms.  Four  essentially  different  unions  are  pos- 
sible ;  namely,  the  fertilisation  of  the  stigma  of  the  long- 
styled  form  by  its  own-form  pollen,  and  by  that  of 
the  short-styled;  and  the  stigma  of  the  short-styled 
form  by  its  own-form  pollen,  and  by  that  of  the  long- 
styled.  The  fertilisation  of  either  form  with  pollen  from 
the  oiher  form  may  be  conveniently  called  a  legitimate 
union,  from  reasons  hereafter  to  be  made  clear ;  and  that 
of  either  form  with  its  own-form  pollen  an  illegitimate 
union.  I  formerly  applied  the  term  "  heteromorphic  " 
to  the  legitimate  unions,  and  "  homomorphic  "  to  the 
illegitimate  unions;  but  after  discovering  the  exist- 
ence of  trimorphic  plants,  in  which  many  more  unions 
are  possible,  these  two  terms  ceased  to  be  applicable. 
The  illegitimate  union  of  both  forms  might  have  been 
tried  in  three  ways;  for  a  flower  of  either  form  may  be 
fertilised  with  pollen  from  the  same  flower,  or  with  that 
from  another  flower  on  the  same  plant,  or  with  that 
from  a  distinct  plant  of  the  same  form.  But  to  make 
my  experiments  perfectly  fair,  and  to  avoid  any  evil 
result  from  self-fertilisation  or  too  close  interbreeding, 
I  have  invariably  employed  pollen  from  a  distinct 
plant  of  the  same  form  for  the  illegitimate  unions  of 
all  the  species;  and  therefore  it  may  be  observed  that 
I  have  used  the  term  "  own-form  pollen  "  in  speaking 
of  such  unions.  The  several  plants  in  all  my  experi- 
ments were  treated  in  exactly  the  same  manner,  and 
were  carefully  protected  by  fine  nets  from  the  access  of 
insects,  excepting  Thrips,  which  it  is  impossible  to  ex- 
clude. I  performed  all  the  manipulations  myself,  and 
weighed  the  seeds  in  a  chemical  balance;  but  during 
many  subsequent  trials  I  followed  the  more  accurate 
plan  of  counting  the  seeds.  Some  of  the  capsules  con- 


CHAP.  I. 


PRIMULA  VERIS. 


25 


tained  no  seeds,  or  only  two  or  three,  and  these  are 
excluded  in  the  column  headed  "good  capsules"  in 
several  of  the  following  tables: — 

TABLE  6. 
Primula  veris. 


Total 

Calculated 

Nature  of  the  Union. 

Number  of 
fertilised. 

Number 
of 
Capsules 
produced. 

Number  of 
good 
Capsules. 

Weight  of 
Seed  in 
grains. 

Weight  of 
SecdLfrorn 
100  good 
Capsulei. 

Long-styled    by   pollen"! 
of   short-styled.      Le-  >• 

22 

15 

14 

8.8 

62 

gitimate  union.     .     .   J 

Long-styled     by     own-  ] 

form  pollen.     Illegiti-  > 

20 

8 

5 

2.1 

42 

mate  union  .     .     .     .    J 

Short-styled   by    pollen  ] 
of    long-styled.      Le-  > 

13 

12 

11 

4.9 

44 

gitimate  union     .    .   J 

Short-styled     by    own-  ] 

form  pollen.     Illegiti-  > 

15 

8 

6 

1.8 

33 

mate  union  .    .     .     .   J 

SUMMAEY  : 

The      two      legitimate  ) 
unions     J 

35 

27 

25 

13.7 

54 

The  ^  two     illegitimate  ) 

35 

16 

11 

3.9 

35 

The  results  may  be  given  in  another  form  (Table  7) 
by  comparing,  first,  the  number  of  capsules,  whether 
good  or  bad,  or  of  the  good  alone,  produced  by  100 
flowers  of  both  forms  when  legitimately  and  illegiti- 
mately fertilised;  secondly,  by  comparing  the  weight 
of  seed  in  100  of  these  capsules,  whether  good  or  bad; 
or,  thirdly,  in  100  of  the  good  capsules. 

We  here  see  that  the  long-styled  flowers  fertilised 

with  pollen  from  the  short-styled  yield  more  capsules, 

especially  good  ones   (i.  e.   containing  more  than  one 

or  two  seeds),  and  that  these  capsules  contain  a  greater 

4 


26 


HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


proportional  weight  of  seeds  than  do  the  flowers  of  the 
long-styled  when  fertilised  with  pollen  from  a  distinct 
plant  of  the  same  form.  So  it  is  with  the  short-styled 
flowers,  if  treated  in  an  analogous  manner.  Therefore  I 
have  called  the  former  method  of  fertilisation  a  legiti- 
mate union  and  the  latter,  as  it  fails  to  yield  the  full 
complement  of  capsules  and  seeds,  an  illegitimate 
union.  These  two  kinds  of  union  are  graphically 
represented  in  Fig.  2. 


TABLE  7. 


Nature  of  th* 
Union. 

Number 
of  Flow- 

"l£"- 

Tf 

SSL 

Number 
of  good 

SSL 

Weight 
of  Sled 
in 
grain.. 

Number 
of 

at 

Weight 
of  i&d 
In 
grain.. 

Number 

'£ 

Weight 
of  S«d 
in 
grains. 

The  two  le-  ) 
gitimate  V 
unions  .  .  J 

100 

77 

71 

39 

100 

50 

100 

54 

Thetwoille-) 
gitimate  [• 
unions  .  .  J 

100 

45 

31 

11 

100 

24 

100 

35 

If  we  consider  the  results  of  the  two  legitimate 
unions  taken  together  and  the  two  illegitimate  ones, 
as  shown  in  Table  7,  we  see  that  the  former  com- 
pared with  the  latter  yielded  capsules,  whether  con- 
taining many  seeds  or  only  a  few,  in  the  proportion  of 
77  to  45,  or  as  100  to  58.  But  the  inferiority  of  the 
illegitimate  unions  is  here  perhaps  too  great,  for  on  a 
subsequent  occasion  100  long-styled  and  short-styled 
flowers  were  illegitimately  fertilised,  and  they  together 
yielded  53  capsules:  therefore  the  rate  of  77  to  53,  or 
as  100  to  69,  is  a  fairer  one  than  that  of  100  to  58. 
Eeturning  to  Table  7,  if  we  consider  only  the  good 
capsules,  those  from  the  two  legitimate  unions  were  to 
those  from  the  two  illegitimate  in  number  as  71  to  31, 
or  as  100  to  44.  Again,  if  we  take  an  equal  number  of 


CHAP.  I. 


PRIMULA  VERIS. 


27 


capsules,  whether  good  or  bad,  from  the  legitimately 
and  illegitimately  fertilised  flowers,  we  find  that  the 
former  contained  seeds  by  weight  compared  with  the 
latter  as  50  to  24,  or  as  100  to  48 ;  but  if  all  the  poor 
capsules  are  rejected,  of  which  many  were  produced 
by  the  illegitimately  fertilised  flowers,  the.  propor- 
tion is  54  to  35,  or  as  100  to  65.  In  this  and  all  other 
cases,  the  relative  fertility  of  the  two  kinds  of  union 


Fig.  2. 

Legitimate  union. 
Complete  fertility. 


Q 


Illegitimate 

union. 

Incomplete 

fertility. 


/ 
! 


Legitimate  union. 
Complete  fertility. 


Illegitimate 
i     union. 
;  Incomplete 
J    fertility. 


ig-styled 
form. 


can,  I  think,  be  judged  of  more  truly  by  the  average 
number  of  seeds  per  capsule  than  by  the  proportion  of 
flowers  which  yield  capsules.  The  two  methods  might 
have  been  combined  by  giving  the  average  number  of 
seeds  produced  by  all  the  flowers  which  were  fertilised, 
whether  they  yielded  capsules  or  not;  but  I  have 
thought  that  it  would  be  more  instructive  always  to 
show  separately  the  proportion  of  flowers  which  pro- 


28        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

duced  capsules,  and  the  average  number  of  apparently 
good  seeds  which  the  capsules  contained. 

Flowers  legitimately  fertilised  set  seeds  under  con- 
ditions which  cause  the  almost  complete  failure  of 
illegitimately  fertilised  flowers.  Thus  in  the  spring  of 
1862  forty  flowers  were  fertilised  at  the  same  time  in 
both  ways.  The  plants  were  accidentally  exposed  in 
the  greenhouse  to  too  hot  a  sun,  and  a  large  number 
of  umbels  perished.  Some,  however,  remained  in  mod- 
erately good  health,  and  on  these  there  were  twelve 
flowers  which  had  been  fertilised  legitimately,  and 
eleven  which  had  been  fertilised  illegitimately.  The 
twelve  legitimate  unions  yielded  seven  fine  capsules, 
containing  on  an  average  each  57.3  good  seeds;  whilst 
the  eleven  illegitimate  unions  yielded  only  two  cap- 
sules, of  which  one  contained  39  seeds,  but  so  poor, 
that  I  do  not  suppose  one  would  have  germinated,  and 
the  other  contained  17  fairly  good  seeds. 

From  the  facts  now  given  the  superiority  of  a  legi- 
timate over  an  illegitimate  union  admits  of  not  the 
least  doubt;  and  we  have  here  a  case  to  which  no 
parallel  exists  in  the  vegetable  or,  indeed,  in  the  ani- 
mal kingdom.  The  individual  plants  of  the  pre- 
sent species,  and  as  we  shall  see  of  several  other 
species  of  Primula,  are  divided  into  two  sets  or 
bodies,  which  cannot  be  called  distinct  sexes,  for 
both  are  hermaphrodites;  yet  they  are  to  a  certain 
extent  sexually  distinct,  for  they  require  reciprocal 
union  for  perfect  fertility.  As  quadrupeds  are  di- 
vided into  two  nearly  equal  bodies  of  different  sexes, 
so  here  we  have  two  bodies,  approximately  equal  in 
numbei,  differing  in  their  sexual  powers  and  related  to 
each  other  like  males  and  females.  There  are  many 
hermaphrodite  animals  which  cannot  fertilise  them- 
selves, but  must  unite  with  another  hermaphrodite.  So 


CHAP.  I.  PRIMULA  VERIS.  29 

it  is  with  numerous  plants;  for  the  pollen  is  often 
mature  and  shed,  or  is  mechanically  protruded,  before 
the  flower's  own  stigma  is  ready;  and  such  flowers  ab- 
solutely require  the  presence  of  another  hermaphro- 
dite for  sexual  union.  But  with  the  cowslip  and  various 
other  species  of  Primula  there  is  this  wide  difference, 
that  one  individual,  though  it  can  fertilise  itself  im- 
perfectly, must  unite  with  another  individual  for  full 
fertility;  it  cannot,  however,  unite  with  any  other 
individual  in  the  same  manner  as  an  hermaphrodite 
plant  can  unite  with  any  other  one  of  the  same  species ; 
or  as  one  snail  or  earth-worm  can  unite  with  any  other 
hermaphrodite  individual.  On  the  contrary,  an  indi- 
vidual belonging  to  one  form  of  the  cowslip  in  order 
to  be  perfectly  fertile  must  unite  with  one  of  the  other 
form,  just  as  a  male  quadruped  must  and  can  unite 
only  with  the  female. 

I  have  spoken  of  the  legitimate  unions  as  being 
fully  fertile;  and  I  am  fully  justified  in  doing  so,  for 
flowers  artificially  fertilised  in  this  manner  yielded 
rather  more  seeds  than  plants  naturally  fertilised  in 
a  state  of  nature.  The  excess  may  be  attributed  to 
the  plants  having  been  grown  separately  in  good  soil. 
With  respect  to  the  illegitimate  union,  we  shall  best 
appreciate  their  degree  of  lessened  fertility  by  the 
following  facts.  Gartner  estimated  the  sterility  of  the 
unions  between  distinct  species,*  in  a  manner  which 
allows  of  a  strict  comparison  with  the  results  of  the 
legitimate  and  illegitimate  unions  of  Primula.  With 
P.  veris,  for  every  100  seeds  yielded  by  the  two 
legitimate  unions,  only  64  were  yielded  by  an  equal 
number  of  good  Capsules  from  the  two  illegitimate 
unions.  With  P.  Sinensis,  as  we  shall  hereafter  see, 


*  '  Versuche  iibcr  die  Bastarderzeugung,'  1849,  p.  216. 


30        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

the  proportion  was  nearly  the  same — namely,  as  100 
to  62.  Now  Gartner  has  shown  that,  on  the  calcula- 
tion of  Verbascum  lynchnitis  yielding  with  its  own  pol- 
len 100  seeds,  it  yielded  when  fertilised  by  the  pollen  of 
V.  Phceniceum  90  seeds;  by  the  pollen  of  V.  nigrum, 
63  seeds;  by  that  of  V.  blattaria,  62  seeds.  So  again, 
Dianthus  barbatus  fertilised  by  the  pollen  of  D.  superbus 
yielded  81  seeds  and  by  the  pollen  of  D.  Japonicus 
66  seeds,  relatively  to  the  100  seeds  produced  by  its 
own  pollen.  We  thus  see — and  the  fact  is  highly  re- 
markable— that  with  Primula  the  illegitimate  unions 
relatively  to  the  legitimate  are  more  sterile  than 
crosses  between  distinct  species  of  other  genera  rela- 
tively to  their  pure  unions.  Mr.  Scott  has  given  *  a 
still  more  striking  illustration  of  the  same  fact:  he 
crossed  Primula  auricula  with  pollen  of  four  other 
species  (P.  Palinuri,  viscosa,  hirsuta,  and  verticillata), 
and  these  hybrid  unions  yielded  a  larger  average  num- 
ber of  seeds  than  did  P.  auricula  when  fertilised  illegiti- 
mately with  its  own-form  pollen. 

The  benefit  which  heterostyled  dimorphic  plants  de- 
rive from  the  existence  of  the  two  forms  is  sufficiently 
obvious,  namely,  the  intercrossing  of  distinct  plants 
being  thus  ensured,  f  Nothing  can  be  better  adapted 
for  this  end  than  the  relative  positions  of  the  anthers 
and  stigmas  in  the  two  forms,  as  shown  in  Fig.  2 ;  but  to 
this  whole  subject  I  shall  recur.  No  doubt  pollen  will 
occasionally  be  placed  by  insects  or  fall  on  the  stigma 
of  the  same  flower;  and  if  cross-fertilisation  fails,  such 
self-fertilisation  will  be  advantageous  to  the  plant,  as 
it  will  thus  be  saved  from  complete  barrenness.  But 
the  advantage  is  not  so  great  as  might  at  first  be 

f'Jonrn.  Linn.  Soc.  Bot.,'  vol.  fertilisation'  how  greatly  the  off- 

vm.,  1864,  p.  93.  spring  from  intercrossed  plants 

T  I  have  shown  in  my  work  on  profit  in  height,  vigour,  and  fer- 

the  'Effects  of  Cross  and  Self-  tility. 


CHAP.  I.  PRIMULA  VERIS.  31 

thought,  for  the  seedlings  from  illegitimate  unions  do 
not  generally  consist  of  both  forms,  but  all  belong  to 
the  parent  form;  they  are,  moreover,  in  some  degree 
weakly  in  constitution,  as  will  be  shown  in  a  future 
chapter.  If,  however,  a  flower's  own  pollen  should  first 
be  placed  by  insects  or  fall  on  the  stigma,  it  by  no 
means  follows  that  cross-fertilisation  will  be  thus  pre- 
vented. It  is  well  known  that  if  pollen  from  a  distinct 
species  be  placed  on  the  stigma  of  a  plant,  and  some 
hours  afterwards  its  own  pollen  be  placed  on  it,  the 
latter  will  be  prepotent  and  will  quite  obliterate  any 
effect  from  the  foreign  pollen;  and  there  can  hardly 
be  a  doubt  that  with  heterostyled  dimorphic  plants, 
pollen  from  the  other  form  will  obligate  the  effects  of 
pollen  from  the  same  form,  even  when  this  has  been 
placed  on  the  stigma  a  considerable  time  before.  To 
test  this  belief,  I  placed  on  several  stigmas  of  a  long- 
styled  cowslip  plenty  of  pollen  from  the  same  plant, 
and  after  twenty-four  hours  added  some  from  a  short- 
styled  dark  red  polyanthus,  which  is  a  variety  of  the 
cowslip.  From  the  flowers  thus  treated  30  seedlings 
were  raised,  and  .all  these,  without  exception,  bore 
reddish  flowers;  so  that  the  effect  of  pollen  from  the 
same  form,  though  placed  on  the  stigmas  twenty-four 
hours  previously,  was  quite  destroyed  by  that  of  pollen 
from  a  plant  belonging  to  the  other  form. 

Finally,  I  may  remark  that  of  the  four  kinds  of 
unions,  that  of  the  ,short-styled  illegitimately  fertilised 
with  its  own-form  pollen  seems  to  be  the  most  sterile  of 
all,  as  judged  by  the  average  number  of  seeds  which 
the  capsules  contained.  A  smaller  proportion,  also,  of 
these  seeds  than  of  the  others  germinated,  and  they 
germinated  more  slowly.  The  sterility  of  this  union  is 
the  more  remarkable,  as  it  has  already  been  shown 
that  the  short-styled  plants  yield  a  larger  number  of 


32        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

seeds  than  the  long-styled,  when  both  forms  are  fer- 
tilised, either  naturally  or  artificially,  in  a  legitimate 
manner. 

In  the  future  chapter,  when  I  treat  of  the  offspring 
from  heterostyled  dimorphic  and  trimorphic  plants 
illegitmately  fertilised  with  their  own-form  pollen,  I 
shall  have  occasion  to  show  that  with  the  present 
species'  and  several  others,  equal-styled  varieties  some- 
times appear. 

PRIMULA  ELATIOR,  Jacq. 

Bardfield  Oxlip  of  English  Authors. 

This  plant,  as  well  as  the  last  or  Cowslip  (P.  veris, 
vel  officinalis),  and  the  Primrose  (P.  vulgaris,  vel  acau- 
lis)  have  been  considered  by  some  botanists  as  varieties 
of  the  same  species.  But  they  are  all  three  undoubtedly 
distinct,  as  will  be  shown  in  the  next  chapter.  The 
present  species  resembles  to  a  certain  extent  in  general 
appearance  the  common  oxlip,  which  is  a  hybrid  be- 
tween the  cowslip  and  primrose.  Primula  elatior  is 
found  in  England  only  in  two  or  three  of  the  eastern 
counties;  and  I  was  supplied  with  living  plants  by  Mr. 
Doubleday,  who,  as  I  believe,  first  called  attention  to 
its  existence  in  England.  It  is  common  in  some  parts 
of  the  Continent ;  and  H.  Miiller  *  has  seen  several 
kinds  of  humble-bees  and  other  bees,  and  Bombylius, 
visiting  the  flowers  in  North  Germany. 

The  results  of  my  trials  on  the  relative  fertility  of 
the  two  forms,  when  legitimately  and  illegitimately 
fertilised,  are  given  in  the  table  on  the  next  page. 

If  we  compare  the  fertilty  of  the  two  legitimate 
unions  taken  together  with  that  of  the  two  illegitimate 


*  '  Die  Befruchtuug  der  Blumen,'  p.  347. 


CHAP.  I. 


PRIMULA  ELATIOR. 


33 


unions  together,  as  judged  by  the  proportional  number 
of  flowers  which  when  fertilised  in  the  two  methods 
yielded  capsules,  the  ratio  is  as  100  to  27;  so  that  by 
this  standard  the  present  species  is  much  more  sterile 
than  P.  veris,  when  both  species  are  illegitimately  fer- 
tilised. If  we  judge  of  the  relative  fertility  of  the  two 
kinds  of  unions  by  the  average  number  of  seeds  per 

TABLE  8. 
Primula  elatior. 


Number 

Number  of 

Minimum 

Nature  of  Union. 

of 
Flowers 
fertilised. 

priced*. 

of  Seed! 

of  Seeds 
in  any  one 

Capsule. 

NumbeTof 
Seeds  per 
Cap.ni;. 

Long-styled    form,     by  1 

pollen  of  short-styled.  > 
Legitimate  union  .     .  J 

10 

6 

62 

34 

46.5 

Long-styled    form,     by  ] 

own-form  pollen.     11-  > 

20 

4 

49* 

2 

27.7 

legitimate  union    .     .  j 

Short-styled    form,    by  ] 
pollen  of  long-styled.  > 
Legitimate  union  .     .  J 

10 

8 

61 

37 

47.7 

Short-styled    form,    by  ) 
own-form  pollen.     11-  V 

17 

3 

19 

9 

12.1 

legitimate  union    .     .  J 

The      two      legitimate  1 
unions  together      .     .  j 

20 

14 

62 

37 

47.1 

The     two     illegitimate  ) 
unions  together      .     .  j 

37 

7 

49* 

2 

35.5 

*  These  seeds  were  so  poor  and  small  that  they  could  hardly  have 
germinated. 

capsule,  the  ratio  is  as  100  to  75.  But  this  latter 
number  is  probably  much  too  high,  as  many  of  the  seeds 
produced  by  the  illegitimately  fertilised  long-styled 
flowers  were  so  small  that  they  probably  would  not 
have  germinated,  and  ought  not  to  have  been  counted. 
Several  long-styled  and  short-styled  plants  were  pro- 
tected from  the  access  of  insects,  and  must  have  been 


34:        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

spontaneously  self-fertilised.  They  yielded  altogether 
only  six  capsules  containing  any  seeds;  and  their 
average  number  was  only  7.8  per  capsule.  Some, 
moreover,  of  these  seeds  were  so  small  that  they  could 
hardly  have  germinated. 

Herr  W.  Breitenbach  informs  me  that  he  examined, 
in  two  sites  near  the  Lippe  (a  tributary  of  the  Khine), 
894  flowers  produced  by  198  plants  of  this  species;  and 
he  found  467  of  these  flowers  to  be  long-styled,  411 
short-styled,  and  16  equal-styled.  I  have  heard  of  no 
other  instance  with  heterostyled  plants  of  equal-styled 
flowers  appearing  in  a  state  of  nature,  though  far  from 
rare  with  plants  which  have  been  long  cultivated.  It 
is  still  more  remarkable  that  in  eighteen  cases  the 
same  plant  produced  both  long-styled  and  short-styled, 
or  long-styled  and  equal-styled  flowers;  and  in  two 
out  of  the  eighteen  cases,  long-styled,  short-styled,  and 
equal-styled  flowers.  The  long-styled  flowers  greatly 
preponderated  on  these  eighteen  plants, — 61  consisting 
of  this  form,  15  of  equal-styled,  and  9  of  the  short- 
styled  form. 

PRIMULA  VULGARIS  (var.  acaulis,  Linn.), 
The  Primrose  of  English  Writers. 

Mr.  J.  Scott  examined  100  plants  growing  near 
Edinburgh,  and  found  44  to  be  long-styled,  and  56 
short-styled;  and  I  took  by  chance  79  plants  in  Kent, 
of  which  39  were  long-styled  and  40  short-styled;  so 
that  the  two  lots  together  consisted  of  83  long-styled 
and  96  short-styled  plants.  In  the  long-styled  form 
the  pistil  is  to  that  of  the  short-styled  in  length,  from 
an  average  of  five  measurements,  as  100  to  51.  The 
stigma  in  the  long-styled  form  is  conspicuously  more 
globose  and  much  more  papillose  than  in  the  short- 


CHAP.  I.  PRIMULA  VULGARIS.  35 

styled,  in  which  latter  it  is  depressed  on  the  summit; 
it  is  equally  broad  in  the  two  forms.  In  both  it  stands 
nearly,  but  not  exactly,  on  a  level  with  the  anthers  of 
the  opposite  form;  for  it  was  found,  from  an  average 
of  15  measurements,  that  the  distance  between  the 
middle  of  the  stigma  and  the  middle  of  the  anthers 
in  the  short-styled  form  is  to  that  in  the  long-styled 

Fig.  3. 


Outlines  of  pollen-grains  of  Primula  vulgaris,  distended  with  water, 
much  magnified  and  drawn  under  the  camera  lucida.  The  upper 
and  smaller  grains  from  the  long-styled  form ;  the  lower  and 
larger  grains  from  the  short-styled. 

as  100  to  93.  The  anthers  do  not  differ  in  size  in  the 
two  forms.  The  pollen-grains  from  the  short-styled 
flowers  before  they  were  soaked  in  water  were  decidedly 
broader,  in  proportion  to  their  length,  than  those  from 
the  long-styled;  after  being  soaked  they  were  relatively 
to  those  from  the  long-styled  as  100  to  71  in  diameter, 
and  more  transparent.  A  large  number  oi  flowers  from 
the  two  forms  were  compared,  and  12  of  the  finest 


HETEKOSTYLED  DIMORPHIC  PLANTS.      CHAP.!. 


flowers  from  each  lot  were  measured,  but  there  was  no 
sensible  difference  between  them  in  size.  Nine  long- 
styled  and  eight  short-styled  plants  growing  together 
in  a  state  of  nature  were  marked,  and  their  capsules 
collected  after  they  had  been  naturally  fertilised;  and 
the  seeds  from  the  short-styled  weighed  exactly  twice 
as  much  as  those  from  an  equal  number  of  long-styled 
plants.  So  that  the  primrose  resembles  the  cowslip  in 
the  short-styled  plants,  being  the  more  productive  of 
the  two  forms.  The  results  of  my  trials  on  the  fer- 
tility of  the  two  forms,  when  legitimately  and  illegiti- 
mately fertilised,  are  given  in  the  following  table : — 

TABLE  9. 
Primula  vulgaris. 


Number 

Maximum 

Minimum 

Nature  of  Union. 

of 
Flowers 

good  Cap- 
sules pro- 

Number of 
Seeds  in  any 

Number  of 
Seeds  in  any 

Numbefof 
Seeds  per 

fertilised. 

duced. 

oneCapsule. 

oneCapsule. 

Cap.uk 

Long-styledform,bypol-  1 
len  from  short-styled.  > 
Legitimate  union  .    .  J 

12 

11 

77 

47 

66.9 

Long-styled    form,     by  ) 
own-form  pollen.    11-  >• 

21 

14 

66 

30 

52.2 

legitimate  union    .     .  J 

Short-styled    form,    by  1 

pollen     from      long-  I 
styled.        Legitimate  | 

8 

7 

75 

48 

65.0 

union   J 

Short-styled    form,    by) 
own-form  pollen.    11-  > 

18 

7 

43 

5 

18.8* 

legitimate  union    .     .  J 

The      two      legitimate  I 
unions  together     .    .  J 

20 

18 

77 

47 

66.0 

The     two     illegitimate  \ 
unions  together     .    .  J 

39 

21 

66 

5 

35.5* 

*  This  average  is  perhaps  rather  too  low. 

We  may  infer  from  this  table  that  the  fertility  of 
the  two  illegitimate  unions  taken  together,  is  to  that  of 


CHAP.  I.  PRIMULA  VULGARIS.  37 

the  two  illegitimate  unions  taken  together,  as  judged  by 
the  proportional  number  of  flowers  which  when  fertilised 
in  the  two  methods  yielded  capsules,  as  100  to  60.  If  we 
judge  by  the  average  number  of  seeds  per  capsule  pro- 
duced by  the  two  kinds  of  unions,  the  ratio  is  as  100 
to  54;  but  this  latter  figure  is  perhaps  rather  too  low. 
It  is  surprising  how  rarely  insects  can  be  seen  during  the 
day  visiting  the  flowers,  but  I  have  occasionally  observed 
small  kinds  of  bees  at  work;  I  suppose,  therefore,  that 
they  are  commonly  fertilised  by  nocturnal  Lepidoptera. 
The  long-styled  plants  when  protected  from  insects 
yield  a  considerable  number  of  capsules,  and  they  thus 
differ  remarkably  from  the  same  form  of  the  cowslip, 
which  is  quite  sterile  under  the  same  circumstances. 
Twenty-three  spontaneously  self-fertilised  capsules  from 
this  form  contained,  on  an  average,  19.2  seeds.  The 
short-styled  plants  produced  fewer  spontaneously  self- 
fertilised  capsules,  and  fourteen  of  them  contained  only 
6.2  seeds  per  capsule.  The  self-fertilisation  of  both 
forms  was  probably  aided  by  Thrips,  which  abounded 
within  the  flowers;  but  these  minute  insects  could  not 
have  placed  nearly  sufficient  pollen  on  the  stigmas,  as 
the  spontaneously  self-fertilised  capsules  contained 
much  fewer  seeds,  on  an  average,  than  those  (as  may  be 
seen  in  Table  9)  which  were  artificially  fertilised  with 
their  own-form  pollen.  But  this  difference  may  perhaps 
be  attributed  in  part  to  the  flowers  in  the  table  having 
been  fertilised  with  pollen  from  a  distinct  plant  be- 
longing to  the  same  form;  whilst  those  which  were 
spontaneously  self-fertilised  no  doubt  generally  received 
their  own  pollen.  In  a  future  part  of  this  volume  some 
observations  will  be  given  on  the  fertility  of  a  red- 
coloured  variety  of  the  primrose. 


38        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


PRIMULA    SINENSIS. 

In  the  long-styled  form  the  pistil  is  about  twice  as 
long  as  that  of  the  short-styled,  and  the  stamens  differ 
in  a  corresponding,  but  reversed,  manner.  The  stigma 
is  considerably  more  elongated  and  rougher  than  that 
of  the  short-styled,  which  is  smooth  and  almost 
spherical,  being  somewhat  depressed  on  the  summit; 
but  the  stigma  varies  much  in  all  its  characters,  the 
result,  probably,  of  cultivation.  The  pollen-grains  of 
the  short-styled  form,  according  to  Hildebrand,*  are 
7  divisions  of  the  micrometer  in  length  and  5  in 
breadth;  whereas  those  of  the  long-styled  are  only 
4  in  length  and  3  in  breadth.  The  grains,  there- 
fore, of  the  short-styled  are  to  those  of  the  long- 
styled  in  length  as  100  to  57.  Hildebrand  also  re- 
marked as  I  had  done  in  the  case  of  P.  veris,  that  the 
smaller  grains  from  the  long-styled  are  much  more 
transparent  than  the  larger  ones  from  the  short-styled 
form.  We  shall  hereafter  see  that  this  cultivated 
plant  varies  much  in  its  trimorphic  condition  and  is 
often  equal-styled.  Some  individuals  may  be  said  to 
be  sub-heterostyled ;  thus  in  two  white-flowered  plants 
the  pistil  projected  above  the  stamens,  but  in  one  of 
them  it  was  longer  and  had  a  more  elongated  and 
rougher  stigma  than  in  the  other;  and  the  pollen-grains 
from  the  latter  were  to  those  from  the  plant  with  a  more 
elongated  pistil  only  as  100  to  88  in  diameter,  instead 
of  as  100  to  57.  The  corolla  of  the  long-styled  and 
short-styled  forms  differs  in  shape,  in  the  same  manner 
as  in  P.  veris.  The  long-styled  plants  tend  to  flower 


*  After  the  appearance  of  my  greatly  about  the  size  of  the  pol- 

paper  this  author  published  some  len-grains  in  the    two    forms.     I 

excellent  observations  on  the  pre-  suppose  that  by  mistake  I  meas- 

sent  species  ('Bot.  Zeitnng,'  Jan.  1,  ured    twice     over     pollen-grains 

1864),  and  he  shows  that  I  erred  from  the  same  form. 


CHAP.  I. 


PRIMULA  SINENSIS. 


39 


before  the  short-styled.  When  both  forms  were  legiti- 
mately fertilised,  the  capsules  from  the  short-styled 
plants  contained,  on  an  average,  more  seeds  than  those 
from  the  long-styled,  in  the  ratio  of  12.2  to  9.3  by 
weight,  that  is,  as  100  to  78.  In  the  following  table 
we  have  the  results  of  two  sets  of  experiments  tried 
at  different  periods: — 

TABLE  10. 
Primula  Sinensis. 


Nature  of  Union. 

Number 

nSL. 

fertilised. 

Number 
of  good 

pCrX£. 

Average 
Weight  of 
Seed,  per 
Capsule. 

Average  Number 

of  Seeds  per 
Capsule,  as 

ascertained  on  a 
'^equcnt 

Long-styled  form,  by  pollen  ) 
of    short-styled.      Legiti-  > 
mate  union      J 

24 

16 

0.58 

50 

Long-styled  form,  by  own-  ] 
form  pollen.    Illegitimate  \ 
union  J 

20 

13 

0.45 

35 

Short-styled  form,  by  pollen  ] 
of  long-styled.  Legitimate  >• 

8 

8 

0.76 

64 

Short-styled  form,  by  own-  ] 
form  pollen.     Illegitimate  /• 
union  J 

• 

4 

0.23 

25 

The  two  legitimate  unions  ) 

32 

24 

0.64 

57 

The  two  illegitimate  unions  \ 
together  j 

27 

17 

0.40 

30 

The  fertility,  therefore,  of  the  two  legitimate  unions 
together  to  that  of  the  two  illegitimate  unions,  as  judged 
by  the  proportional  number  of  flowers  which  yielded 
capsules,  is  as  100  to  84.  Judging  by  the  average 
weight  of  seeds  per  capsule  produced  by  the  two  kinds 
of  unions,  the  ratio  is  as  100  to  63.  On  another  occa- 
sion a  large  number  of  flowers  of  both  forms  were 


40        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


fertilised  in  the  same  manner,  but  no  account  of  their 
number  was  kept.  The  seeds,  however,  were  carefully 
counted  and  the  averages  are  shown  in  the  right-hand 
column.  The  ratio  for  the  number  of  seeds  produced 
by  the  two  legitimate  compared  with  the  two  illegiti- 
mate unions  is  here  100  to  53,  which  is  probably  more 
accurate  than  the  foregoing  one  of  100  to  63. 

Hildebrand  in  the  paper  above  referred  to  gives  the 
results  of  his  experiments  on  the  present  species;  and 
these  are  shown  in  a  condensed  form  in  the  accompany- 
ing table : — 

TABLE  11. 
Primula  Sinensis  (from  Hildebrand). 


Nature  of  Union. 

Number 

FC'er, 
fertilised. 

Number 
of  good 
Capsules 
produced. 

Average 
Number  of 

OfJET 

Long-styled    form,   by   pollen    of  short-  j 
styled.    Legitimate  union    j 

14 

14 

41 

Long-styled  form,   by  own-form  pollen,  ~) 
from   a    distinct    plant.      Illegitimate  !• 
union     J 

26 

26 

18 

Long-styled  form,  by  pollen  from  same  ) 
flower.    Illegitimate  union  j 

27 

21 

17 

Short-styled    form,    by    pollen    of    long-  ) 
styled.     Legitimate  union    j 

14 

14 

44 

Short-styled  form,   by  own-form  pollen,  ) 
from  a  distinct  plant.   Illegitimate  union  j 

16 

16 

20 

Short-styled,   by  pollen  from   the    same  ) 
flower.     Illegitimate  union  j 

21 

11 

8 

The  two  legitimate  unions  together     . 

28 

28 

43 

The    two    illegitimate    unions    together  1 
(own-form  pollen)  .     .                               { 

42 

42 

18 

The  two  illegitimate  unions  together  (pol-  ) 
len  from  the  same  flower)     .     .     .     .     .  } 

48 

32 

13 

Besides  using  for   the   illegitimate   unions   pollen 
from  a  distinct  plant  of  the  same  form,  as  was  always 


CHAP.  I.  PRIMULA  SINENSIS.  41 

done  by  me,  he  tried,  in  addition,  the  effects  of  the 
plant's  own  pellen.    He  counted  the  seeds. 

It  is  remarkable  that  here  all  the  flowers  which 
were  fertilised  legitimately,  as  well  as  those  fertilised 
illegitimately  with  pollen  from  a  distinct  plant  be- 
longing to  the  same  form,  yielded  capsules;  and  from 
this  fact  it  might  be  inferred  that  the  two  forms  were 
reciprocally  much  more  fertile  in  his  case  than  in 
mine.  But  his  illegitimately  fertilised  capsules  from 
both  forms  contained  fewer  seeds  relatively  to  the 
legitimately  fertilised  capsules  than  in  my  experi- 
ments; for  the  ratio  in  his  case  is  as  42  to  100, 
instead  of,  as  in  mine,  as  53  to  100.  Fertility  is  a 
very  variable  element  with  most  plants,  being  deter- 
mined by  the  conditions  to  which  they  are  subjected,  of 
which  fact  I  have  observed  striking  instances  with  the 
present  species;  and  this  may  account  for  the  differ- 
ence between  my  results  and  those  of  Hildebrand.  His 
plants  were  kept  in  a  room,  and  perhaps  were  grown  in 
too  small  pots  or  under  some  other  unfavourable  condi- 
tions, for  his  capsules  in  almost  every  case  contained 
a  smaller  number  of  seeds  than  mine,  as  may  be  seen 
by  comparing  the  right-hand  columns  in  Tables  10 
and  11. 

The  most  interesting  point  in  Hildebrand's  experi- 
ments is  the  difference  in  the  effects  of  illegitimate 
fertilisation  with  a  flower's  own  pollen,  and  with  that 
from  a  distinct  plant  of  the  same  form.  In  the  latter 
case  all  the  flowers  produced  capsules,  whilst  only  67 
out  of  100  of  those  fertilised  with  their  own  pollen 
produced  capsules.  The  self-fertilised  capsules  also  con- 
tained seeds,  as  compared  with  capsules  from  flowers 
fertilised  with  pollen  from  a  distinct  plant  of  the  same 
form,  in  the  ratio  of  72  to  100. 

In  order  to  ascertain  how  far  the  present  species  was 


42        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

spontaneously  self-fertile,  live  long-styled  plants  were 
protected  by  me  from  insects;  and  they* bore  up  to  a 
given  period  147  flowers  which  set  62  capsules;  but 
many  of  these  soon  fell  off,  showing  that  they  had  not 
been  properly  fertilised.  At  the  same  time  five  short- 
styled  plants  were  similarly  treated,  and  they  bore  116 
flowers  which  ultimately  produced  only  seven  capsules. 
On  another  occasion  13  protected  long-styled  plants 
yielded  by  weight  25.9  grains  of  spontaneously  self- 
fertilised  seeds.  At  the  same  time  seven  protected 
short-styled  plants  yielded  only  half-a-grain  weight  of 
seeds.  Therefore  the  long-styled  plants  yielded  nearly 
24  times  as  many  spontaneously  self-fertilised  seeds  as 
did  the  same  number  of  short-styled  plants.  The  chief 
cause  of  this  great  difference  appears  to  be,  that  when 
the  corolla  of  a  long-styled  plant  falls  off,  the  anthers, 
from  being  situated  near  the  bottom  of  the  tube,  are 
necessarily  dragged  over  the  stigma  and  leave  pollen 
on  it,  as  I  saw  when  I  hastened  the  fall  of  nearly 
withered  flowers;  whereas,  in  the  short-styled  flowers, 
the  stamens  are  seated  at  the  mouth  of  the  corolla, 
and  in  falling  off  do  not  brush  over  the  lowly-seated 
stigmas.  Hildebrand  likewise  protected  some  long- 
styled  and  short-styled  plants,  but  neither  ever  yielded 
a  single  capsule.  He  thinks  that  the  difference  in  our 
results  may  be  accounted  for  by  his  plants  having  been 
kept  in  a  room  and  never  having  been  shaken;  but 
this  explanation  seems  to  me  doubtful;  his  plants  were 
in  a  less  fertile  condition  than  mine,  as  shown  by 
the  difference  in  the  number  of  seeds  produced,  and  it 
is  highly  probable  that  their  lessened  fertility  would 
have  interfered  with  especial  force  with  their  capacity 
for  producing  self-fertilised  seeds. 


CHAP.  I.  PRIMULA  AURICULA.  43 


PRIMULA  AURICULA.* 

This  species  is  heterostyled,  like  the  preceding  ones ;  but 
amongst  the  varieties  distributed  by  florists  the  long-styled 
form  is  rare,  as  it  is  not  valued.  There  is,  a  much  greater 
relative  inequality  in  the  length  of  the  pistil  and  stamens  in 
the  two  forms  of  the  auricula  than  in  the  cowslip ;  the  pistil 
in  the  long-styled  being  nearly  four  times  as  long  as  that  in 
the  short-styled,  in  which  it  is  barely  longer  than  the 
ovarium.  The  stigma  is  nearly  of  the  same  shape  in  both 
forms,  but  is  rougher  in  the  long-styled,  though  the  differ- 
ence is  not  so  great  as  between  the  two  forms  of  the  cowslip. 
In  the  long-styled  plants  the  stamens  are  very  short,  rising 
but  little  above  the  ovarium.  The  pollen-grains  of  these 
short  stamens,  when  distended  with  water,  were  barely 
•BW&  of  an  inch  in  diameter,  whereas  those  from  the  long 
stamens  of  the  short-styled  plants  were  barely  roW,  show- 
ing a  relative  difference  of  about  71  to  100.  The  smaller 
grains  of  the  long-styled  plants  are  also  much  more  trans- 
parent, and  before  distension  with  water  more  triangular 
in  outline  than  those  of  the  other  form.  Mr.  Scott  f  com- 
pared ten  plants  of  both  forms  growing  under  similar  con- 
ditions, and  found  that,  although  the  long-styled  plants 
produced  more  umbels  and  more  capsules  than  the  short- 
styled,  yet  they  yielded  fewer  seeds,  in  the  ratio  of  66  to 
100.  Three  short-styled  plants  were  protected  by  me  from 
the  access  of  insects,  and  they  did  not  produce  a  single  seed. 
Mr.  Scott  protected  six  plants  of  both  forms,  and  found 
them  excessively  sterile.  The  pistil  of  the  long-styled  form 
stands  so  high  above  the  anthers,  that  it  is  scarcely  possible 
that  pollen  should  reach  the  stigma  without  some  "aid; 
and  one  of  Mr.  Scott's  long-styled  plants  which  yielded 
a  few  seeds  (only  18  in  number)  was  infested  by  aphides, 


*  According  to  Kerner,  our  gar-  and  the  short-  styled  98  seeds  per 

den  auriculas  are  descended  from  capsule:  see  his  "Geschichte  der 

P.  pubescens,  Jacq.,  which  is  a  hy-  Aurikel,"  'Zeitschr.  des  Deutsch- 

brid  between  the  true  P.  auricula  en  undOest.  Alpen-Vereins,'  Band 

and  hirsuta.    This  hybrid  has  now  vi.  p.  52.     Also  '  Die  Primulaceen- 

been    propagated    for   about    300  Bastarten,'  'Oest.  Bot.  Zeitschrift,' 

years,  and  produces,  when  legiti-  1835,  Nos.  3,  4,  and  5. 

mately  fertilised,  a  large  number  t  '  Journ.  Linn.  Soc.  Bot.,'  vol. 

of  seeds  ;    the  long-styled   forms  viii.,  1864,  p.  86. 
yielding  an  average  number  of  73, 


44        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  L 

and  he  does  not  doubt  that  these  had  imperfectly  ferti- 
lised it. 

I  tried  a  few  experiments  by  reciprocally  fertilising  the 
two  forms  in  the  same  manner  as  before,  but  my  plants 
were  unhealthy,  so  I  will  give,  in  a  condensed  form,  the 
results  of  Mr.  Scott's  experiments.  For  fuller  particulars 
with  respect  to  this  and  the  five  following  species,  the  paper 
lately  referred  to  may  be  consulted.  In  each  case  the  fer- 
tility of  the  two  legitimate  unions,  taken  together,  is  com- 
pared with  that  of  the  two  illegitimate  unions  together, 
by  the  same  two  standards  as  before,  namely,  by  the  pro- 
portional number  of  flowers  which  produced  good  capsules, 
and  by  the  average  number  of  seeds  per  capsule.  The  fer- 
tility of  the  legitimate  unions  is  always  taken  at  100. 

By  the  first  standard,  the  fertility  of  the  two  legitimate 
unions  of  the  auricula  is  to  that  of  the  two  illegitimate 
unions  as  100  to  80;  and  by  the  second  standard  as  100 
to  15. 

PRIMULA  SIKKIMENSIS. 

According  to  Mr.  Scott,  the  pistil  of  the  long-styled 
form  is  fully  four  times  as  long  as  that  of  the  short-styled, 
but  their  stigmas  are  nearly  alike  in  shape  and  roughness. 
The  stamens  do  not  differ  so  much  in  relative  length  as  the 
pistils.  The  pollen-grains  differ  in  a  marked  manner  in  the 
two  forms;  "those  of  the  long-styled  plants  ire  sharply 
triquetrous,  smaller,  and  more  transparent  than  those  of 
the  short-styled,  which  are  of  a  bluntly  triangular  form." 
The  fertility  of  the  two  legitimate  unions  to  that  of  the  two 
illegitimate  unions  is  by  the  first  standard  as  100  to  95, 
and  by  the  second  standard  as  100  to  31. 


PRIMULA  CORTUSOIDES. 

The  pistil  of  the  long-styled  form  is  about  thrice  as  long 
as  that  of  the  short-styled,  the  stigma  being  double  as  long 
and  covered  with  much  longer  papillae.  The  pollen-grains 
of  the  short-styled  form  are,  as  usual,  "  larger,  less  trans- 
parent, and  more  bluntly  triangular  than  those  from  the 
long-styled  plants."  The  fertility  of  the  two  legitimate 
unions  to  that  of  the  two  illegitimate  unions  is  by  the  first 


CHAP.  I.  SUMMARY  ON  PRIMULA.  45 

standard  as  100  to  74,  and  by  the  second  standard  as  100 
to  66. 

PRIMULA  INVOLUCRATA. 

The  pistil  of  the  long-styled  form  is  about  thrice  as 
long  as  that  of  the  short-styled ;  the  stigma  of  the  former  is 
globular  and  closely  beset  with  papilla,  whilst  that  of  the 
short-styled  is  smooth  and  depressed  on  the  apex.  The 
pollen-grains  of  the  two  forms  differ  in  size  and  trans- 
parency as  before,  but  not  in  shape.  The  fertility  of  the 
two  legitimate  to  that  of  the  two  illegitimate  unions  is  by 
the  first  standard  as  100  to  72 ;  and  by  the  second  standard 
as  100  to  47. 

PRIMULA   FARINOSA. 

According  to  Mr.  Scott,  the  pistil  of  the  long-styled 
form  is  only  about  twice  as  long  as  that  of  the  short-styled. 
The  stigmas  of  the  two  forms  differ  but  little  in  shape.  The 
pollen-grains  differ  in  the  usual  manner  in  size,  but  not  in 
form.  The  fertility  of  the  two  legitimate  to  that  of  the  two 
illegitimate  unions  is  by  the  first  standard  as  100  to  71,  and 
by  the  second  standard  as  100  to  44. 


Summary  on  the  foregoing  heterostyled  species  of 
Primula. — The  fertility  of  the  long  and  short-styled 
plants  of  the  above  species  of  Primula,  when  the  two 
forms  are  fertilised  legitimately,  and  illegitimately  with 
pollen  of  the  same  form  taken  from  a  distinct  plant, 
has  now  been  given.  The  results  are  seen  in  the  fol- 
lowing table;  the  fertility  being  judged  by  two  stand- 
ards, namely,  by  that  of  the  proportional  number  of 
flowers  which  yielded  capsules,  and  by  that  of  the  aver- 
age number  of  seeds  per  capsule.  But  for  full  accu- 
racy many  more  observations,  under  varied  conditions, 
would  be  requisite. 

With  plants  of  all  kinds  some  flowers  generally  fail 
to  produce  capsules,  from  various  accidental  causes; 
but  this  source  of  error  has  been  eliminated,  as  far  as 


46        HETEROSTYLED  DIMORPHIC   PLANTS.      CHAP.  I. 

possible,  in  all  the  previous  cases,  by  the  manner  in 
which  the  calculations  have  been  made.  Supposing, 
for  instance,  that  20  flowers  were  fertilised  legiti- 
mately and  yielded  18  capsules,  and  that  30  flowers 
were  fertilised  illegitimately  and  yielded  15  cap- 
sules, we  may  assume  that  on  an  average  an  equal 


TABLE  12. 

Summary  on  the  Fertility  of  the  two  Legitimate  Unions, 
compared  with  that  of  the  two  Illegitimate  Unions, 
in  the  genus  Primula.  The  former  taken  at  100. 


Name  of  Specie* 

Illegitimate  Unions. 

Judged  of  by  th« 
Proportional  Number 
of  Flowers  which, 
produced  Capsule.. 

Judged  of  by  the  Average 
Number  (or  V/cigM  In 
some  CMOS)  of  Seed, 
per  Capsule. 

Primula  veris    

27 

60 
84 
? 
10 
80 
95 
74 
72 
71 

„.  f  (Probably 
'    1  too  high.) 
M  (  (Probably 
54  1  too  low.) 
63 

53 
42 
15 
31 
66 
48 
44 

P  elatior       .    .         . 

P  vulgaris 

P.  Sinensis    

(second  trial)      .    . 
"        (after  Hildebrand  )  . 
P.  auricula  (Scott)  

P.  Sikkimensis  (Scott)    .     .     . 
P.  cortusoides  (Scott)      .    .     . 
P.  involucrata  (Scott)    .    .     . 
P.  farinosa  (Scott)      .    .    .    . 

Average  of  the  nine  species  . 

88.4 

61.8 

proportion  of  the  flowers  in  both  lots  would  fail  to 
produce  capsules  from  various  accidental  causes;  and 
the  ratio  of  %$  to  fa  or  as  100  to  56  (in  whole 
numbers),  would  show  the  proportional  number  of  cap- 
sules due  to  the  two  methods  of  fertilisation;  and  the 
number  56  would  appear  in  the  left-hand  column 


CHAP.  I.  SUMMARY  ON  PRIMULA.  47 

of  Table  12,  and  in  my  other  tables.  With  respect 
to  the  average  number  of  seeds  per  capsule  hardly 
anything  need  be  said:  supposing  that  the  legiti- 
mately fertilised  capsules  contained,  on  an  average, 
50  seeds,  and  the  illegitimately  fertilised  capsules 
25  seeds;  then  as  50  is  to  25  so  is  100  to  50;  and 
the  latter  number  would  appear  in  the  right-hand 
column. 

It  is  impossible  to  look  at  the  above  table  and  doubt 
that  the  legitimate  unions  between  the  two  forms  of  the 
above  nine  species  of  Primula  are  much  more  fertile 
than  the  illegitimate  unions;  although  in  the  latter 
case  pollen  was  always  taken  from  a  distinct  plant  of 
the  same  form.  There  is,  however,  no  close  corre- 
spondence in  the  two  rows  of  figures,  which  give,  ac- 
cording to  the  two  standards,  the  difference  of  fertility 
between  the  legitimate  and  illegitimate  unions.  Thus 
all  the  flowers  of  P.  Sinensis  which  were  illegitimately 
fertilised  by  Hildebrand  produced  capsules;  but  these 
contained  only  42  per  cent,  of  the  number  of  seeds 
yielded  by  the  legitimately  fertilised  capsules.  So 
again,  95  per  cent,  of  the  illegitimately  fertilised 
flowers  of  P.  Sikkimensis  produced  capsules;  but  these 
contained  only  31  per  cent,  of  the  number  of  seeds  in 
the  legitimate  capsules.  On  the  other  hand,  with 
P.  elatior  only  27  per  cent,  of  the  illegitimately  fer- 
tilised flowers  yielded  capsules;  but  these  contained 
nearly  75  per  cent,  of  the  legitimate  number  of  seeds. 
It  appears  that  the  setting  of  the  flowers,  that  is,  the 
production  of  capsules  whether  good  or  bad,  is  not 
so  much  influenced  by  legitimate  and  illegitimate  fer- 
tilisation as  is  the  number  of  seeds  which  the  capsules 
contain.  For,  as  may  be  seen  at  the  bottom  of 
Table  12,  88.4  per  cent,  of  the  illegitimately  fertilised 
flowers  yielded  capsules;  but  these  contained  only 


48        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


61.8  per  cent,  of  seeds,  in  comparison,  in  each,  case, 
with  the  legitimately  fertilised  flowers  and  capsules 
of  the  same  species. 

There  is  another  point  which  deserves  notice, 
namely,  the  relative  degree  of  infertility  in  the  several 
species  of  the  long-styled  and  short-styled  flowers, 
when  both  are  illegitimately  fertilised.  The  data 
may  be  found  in  the  earlier  tables,  and  in  those  given 
by  Mr.  Scott  in  the  Paper  already  referred  to.  If  we 
call  the  number  of  seeds  per  capsule  produced  by  the 
illegitimately  fertilised  long-styled  flowers  100,  the 
seeds  from  the  illegitimately  fertilised  short-styled 
flowers  will  be  represented  by  the  following  num- 
bers:— 


Primula  veris .     71 


P.  elatior    . 

P.  vulgaris 
P.  Sinensis 


.     44 


(Probably 
too  low. ) 
(Perhaps 
too  low.) 


Primula  auricula  ....  119 
P.  Sikkimensis     ....     57 

P.  cortusoidcs 93 

P.  involucrata 74 

P.  farinosa  .  .    63 


We  thus  see  that,  with  the  exception  of  P.  auricula,  the 
long-styled  flowers  of  all  nine  species  are  more  fertile 
than  the  short-styled  flowers,  when  both  forms  are  il- 
legitimately fertilised.  Whether  P.  auricula  really 
differs  from  the  other  species  in  this  respect  I  can  form 
no  opinion,  as  the  result  may  have  been  accidental. 
The  degree  of  self-fertility  of  a  plant  depends  on  two 
elements,  namely,  on  the  stigma  receiving  its  own  pollen 
and  on  its  more  or  less  efficient  action  when  placed 
there.  Now,  as  the  anthers  of  the  short-styled  flowers 
of  several  species  of  Primula  stand  directly  above  the 
stigma,  their  pollen  is  more  likely  to  fall  on  it,  or  to 
be  carried  down  to  it  by  insects,  than  in  the  case  of 
the  long-styled  form.  It  appears  probable,  therefore, 
at  first  sight,  that  the  lessened  capacity  of  the  short- 
styled  flowers  to  be  fertilised  with  their  own  pollen,  is 


CHAP.  I.  HOMOSTYLED  PRIMULAS.  49 

a  special  adaptation  for  counteracting  their  greater 
liability  to  receive  their  own  pollen,  and  thus  for 
checking  self-fertilisation.  But  from  facts  with  respect 
to  other  species  hereafter  to  be  given,  this  view  can 
hardly  be  admitted.  In  accordance  with  the  above 
liability,  when  some  of  the  species  of  Primula  were 
allowed  to  fertilise  themselves  spontaneously  under 
a  net,  all  insects  being  excluded,  except  such  minute 
ones  as  Thrips,  the  short-styled  flowers,  notwith- 
standing their  greater  innate  self-sterility,  yielded 
more  seed  than  did  the  long-styled.  None  of  the 
species,  however,  when  insects  were  excluded,  made  a 
near  approach  to  full  fertility.  But  the  long-styled 
form  of  P.  Sinensis  gave,  under  these  circumstances, 
a  considerable  number  of  seeds,  as  the  corolla  in  falling 
off  drags  the  anthers,  which  are  seated  low  down  in 
the  tube,  over  the  stigma,  and  thus  leaves  plenty  of 
pollen  on  it. 

Homostyled  species  of  Primula. — It  has  now  been 
shown  that  nine  of  the  species  in  this  genus  exist  under 
two  forms,  which  differ  not  only  in  structure  but  in 
function.  Besides  these  Mr.  Scott  enumerates  27  other 
species  *  which  are  heterostyled ;  and  to  these  probably 
others  will  be  hereafter  added.  Nevertheless,  some 
species  are  homostyled;  that  is,  they  exist  only  under 
a  single  form;  but  much  caution  is  necessary  on  this 
head,  as  several  species  when  cultivated  are  apt  to 
become  equal-styled.  Mr.  Scott  believes  that  P. 
Scoiica,  verticillata,  a  variety  of  Sibirica,  elata,  mollis, 
and  longiflora,\  are  truly  homostyled ;  and  to  these  many 


*  H.  Miiller  has  given  in  '  Na-  f  Koch  was  aware  that  this  spe- 

ture,' Dec.  10, 1874,  p.  110,  a  draw-  cies  was  homostyled:   see   "Tre- 

ing  of  one  of  these  species,  viz.  the  viranus    iiher   Dichogamie    nach 

Alpine  P.  rillosa,  and  shows  that  it  Sprengel  und  Darwin,"  'Bot.  Zei- 

is  fertilised  exclusively  by  Lepi-  tung,'  Jan.  2,  1863,  p.  4. 
doptera. 


50        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

be  added,  according  to  Axell,  P.  stricta.  Mr.  Scott  ex- 
perimented on  P.  Scotica,  mollis,  and  verticillata,  and 
found  that  their  flowers  yielded  an  abundance  of  seeds 
when  fertilised  with  their  own  pollen.  This  shows 
that  they  are  not  heterostyled  in  function.  P.  Scotica 
is,  however,  only  moderately  fertile  when  insects  are 
excluded,  but  this  depends  merely  on  the  coherent 
pollen  not  readily  falling  on  the  stigma  without  their 
aid.  Mr.  Scott  also  found  that  the  capsules  of  P. 
verticillata  contained  rather  more  seed  when  the  flowers 
were  fertilised  with  pollen  from  a  distinct  plant  than 
when  with  their  own  pollen;  and  from  this  fact  he  in- 
fers that  they  are  sub-heterostyled  in  function,  though 
not  in  structure.  But  there  is  no  evidence  that  two 
sets  of  individuals  exist,  which  differ  slightly  in  func- 
tion and  are  adapted  for  reciprocal  fertilisation;  and 
this  is  the  essence  of  heterostylism.  The  mere  fact 
of  a  plant  being  more  fertile  with  pollen  from  a  dis- 
tinct individual  than  with  its  own  pollen,  is  common 
to  very  many  species,  as  I  have  shown  in  my  work  "  On 
the  Effects  of  Cross  and  Self-fertilisation." 

HOTTONIA   PALUSTRIS. 

This  aquatic  member  of  the  Primulaceae  is  con- 
spicuously heterostyled,  as  the  pistil  of  the  long-styled 
form  projects  far  out  of  the  flower,  the  stamens  being 
enclosed  within  the  tube;  whilst  the  stamens  of  the 
short-styled  flower  project  far  forwards,  the  pistil  being 
enclosed.  This  difference  between  the  two  forms  has 
attracted  the  attention  of  various  botanists,  and  that 
of  Sprengel,*  in  1793,  who,  with  his  usual  sagacity, 
adds  that  he  does  not  believe  the  existence  of  the  two 
forms  to  be  accidental,  though  he  cannot  explain  their 


*  'Das  entdecke  Geheiinniss  der  Natur,'  p.  103. 


CHAP.  I.  HOTTONIA  PALUSTRIS.  51 

purpose.  The  pistil  of  the  long-styled  form  is  more 
than  twice  as  long  as  that  of  the  short-styled,  with  the 
stigma  rather  smaller,  though  rougher.  H.  Miiller  * 
gives  figures  of  the  stigmatic  papillae  of  the  two  forms, 
and  those  of  the  long-styled  are  seen  to  be  more  than 
double  the  length,  and  much  thicker  than  the  papillae 
of  the  short-styled  form.  The  anthers  in  the  one  form 
do  not  stand  exactly  on  a  level  with  the  stigma  in 
the  other  form;  for  the  distance  between  the  organs 
is  greater  in  the  short-styled  than  in  the  long-styled 
flowers  in  the  proportion  of  100  to  71.  In  dried  speci- 
mens soaked  in  water  the  anthers  of  the  short-styled 
form  are  larger  than  those  of  the  long-styled,  in  the 
ratio  of  100  to  83.  The  pollen-grains,  also,  from  the 
short-styled  flowers  are  conspicuously  larger  than  those 
from  the  long-styled;  the  ratio  between  the  diameters 
of  the  moistened  grains  being  as  100  to  64,  according 
to  my  measurements,  but  according  to  the  measure- 
ments of  H.  Miiller  as  100  to  61 ;  and  his  are  probably 
the  more  accurate  of  the  two.  The  contents  of  the 
larger  pollen-grains  appear  more  coarsely  granular 
and  of  a  browner  tint,  than  those  in  the  smaller 
grains.  The  two  forms  of  Hottonia  thus  agree  closely 
in  most  respects  with  those  of  the  heterostyled  species 
of  Primula.  The  flowers  of  Hottonia  are  cross-ferti- 
lised, according  to  Miiller,  chiefly  by  Diptera. 

Mr.  Scott  f  made  a  few  trials  on  a  short-styled  plant, 
and  found  that  the  legitimate  unions  were  in  all  ways 
more  fertile  than  the  illegitimate;  but  since  the  pub- 
lication of  his  paper  H.  Miiller  has  made  much  fuller 
experiments,  and  I  give  his  results  in  the  follow- 
ing table,  drawn  up  in  accordance  with  my  usual 
plan : — 

*'Die  Befruchtung,'  &c.,  page       t  'Journ.  Linn.  Soc.  Bot.,' vol. 
350.  viii.,  1864,  p.  79. 


52        HETEKOSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 


TABLE  13. 
Hottonia  palustris  (from  H.  Mutter). 


Nature  of  Union. 

Number 
of  Capsulei 
examined. 

Average 
Numb.?  of 
Seeds  per 
fapiuie. 

Long-styled  form,  by  pollen  of  short-styled.    Le-  ) 

34 

91.4 

Long-styled  form,  by  own-form  pollen,  from  a  dis-  1 
tinct  plant.     Illegitimate  union     j 

18 

77.5 

Short-styled  form,  by  pollen  of  long-styled.     Le-  1 

30 

66.2 

Short-styled  form,  by  own-form  pollen,  from  a  dis-  ) 
tinct  plant.    Illegitimate  union     j 

19 

18.7 

64 

78.8 

The  two  illegitimate  unions  together    

37 

48.1 

The  most  remarkable  point  in  this  table  is  the  small 
average  number  of  seeds  from  the  short-styled  flowers 
when  illegitimately  fertilised,  and  the  unusually  large 
average  number  of  seeds  yielded  by  the  illegitimately 
fertilised  long-styled  flowers,  relatively  in  both  cases  to 
the  product  of  the  legitimately  fertilised  flowers.*  The 
two  legitimate  unions  compared  with  the  two  il- 
legitimate together  yield  seeds  in  the  ratio  of  100 
to  61. 

H.  Miiller  also  tried  the  effects  of  illegitimately  fer- 
tilising the  long-styled  and  short-styled  flowers  with 
their  own  pollen,  instead  of  with  that  from  another 


*H.  Miiller  says  ('Die  Be- 
fruchtung.'  &c.,  p.  352)  that  the 
long-styled  flowers,  when  illegiti- 
mately fertilised,  yield  as  many 
seeds  as  when  legitimately  fer- 
tilised;  but  by  adding  up  the 
number  of  seeds  from  all  the  cap- 
sules produced  by  the  two  methods 
of  fertilisation,  as  given  by  him, 


I  arrive  at  the  results  shown  in 
Table  13.  The  average  number 
in  the  long-styled  capsules,  when 
legitimately  fertilised,  is  91.4, 
and  when  illegitimately  fertilised, 
77.5 ;  or  as  100  to  85.  H.  Miiller 
agrees  with  me  that  this  is  the 
proper  manner  of  viewing  the 


CHAP.  I.  ANDROSACE.  53 

plant  of  the  same  form;  and  the  results  are  very 
striking.  For  the  capsules  from  the  long-styled  flowers 
thus  treated  contained,  on  an  average,  only  15.7  seeds 
instead  of  77.5;  and  those  from  the  short-styled  6.5 
instead  of  18.7  seeds  per  capsule.  The  number  6.5 
agrees  closely  with  Mr.  Scott's  result  from  the  same 
form  similarly  fertilised. 

From  some  observations  by  Dr.  Torrey,  Hottonia 
inflata,  an  inhabitant  of  the  United  States,  does  not 
appear  to  be  heterostyled,  but  is  remarkable  from  pro- 
ducing cleistogamic  flowers,  as  will  be  seen  in  the  last 
chapter  of  this  volume. 

Besides  the  general  Primula  and  Hottonia,  Andro- 
sace  (vel  Gregoria,  vel  Aretia)  vitalliana  is  heterostyled. 
Mr.  Scott  *  fertilised  with  their  own  pollen  21  flowers 
on  three  short-styled  plants  in  the  Edinburgh  Botanic 
Gardens,  and  not  one  yielded  a  single  seed;  but 
eight  of  them,  which  were  fertilised  with  pollen  from 
one  of  the  other  plants  of  the  same  form,  set  two  empty 
capsules.  He  was  able  to  examine  only  dried  speci- 
mens of  the  long-styled  forms.  But  the  evidence  seems 
sufficient  to  leave  hardly  a  doubt  that  Androsace  is 
heterostyled.  Fritz  Miiller  sent  me  from  South  Brazil 
dried  flowers  of  a  Statice  which  he  believed  to  be  heter- 
ostyled. In  the  one  form  the  pistil  was  considerably 
longer  and  the  stamens  slightly  shorter  than  the  corre- 
sponding organs  in  the  other  form.  But  as  in  the 
shorter-styled  form  the  stigmas  reached  up  to  the 
anthers  of  the  same  flower,  and  as  I  could  not  detect  in 
the  dried  specimens  of  the  two  forms  any  difference 
in  their  stigmas,  or  in  the  size  of  their  pollen-grains,  I 
dare  not  rank  this  plant  as  heterostyled.  From  state- 


*  See  also  "  Treviranus  "  in  'Bot.  Zeitung,'  1863,  p.  6,  on  this  plant 
being  dimorphic. 


54        HETEROSTYLED  DIMORPHIC  PLANTS.      CHAP.  I. 

ments  made  by  Vaucher  I  was  led  to  think  that  Solda- 
nella  alpina  was  heterostyled,  but  it  is  impossible  that 
Kerner,  who  has  closely  studied  this  plant,  could  have 
overlooked  the  fact.  So  again  from  other  statements  it 
appeared  probable  that  Pyrola  might  be  heterostyled, 
but  H.  Miiller  examined  for  me  two  species  in  North 
Germany,  and  found  this  not  to  be  the  case. 


CHAP.  II.  HYBRID  PRIMULAS.  55 


CHAPTER    II. 
HYBRID  PBIMULAS. 

The  Oxlip  a  hybrid  naturally  produced  between  Primula  veris  and 
vulgaris— The  differences  in  structure  and  function  between  tho 
two  parent-species — Effects  of  crossing  long-styled  and  shortrstyled 
Oxlips  with  one  another  and  with  the  two  forms  of  both  parent- 
species — Character  of  the  offspring  from  Oxlips  artificially  self-fer- 
tilised and  cross-fertilised  in  a  state  of  nature— Primula  elatior 
shown  to  be  a  distinct  species — Hybrids  between  other  heterostyled 
species  of  Primula— Supplementary  note  on  spontaneously  produced 
hybrids  in  the  genus  Verbascum. 

THE  various  species  of  Primula  have  produced  in  a 
state  of  nature  throughout  Europe  an  extraordinary 
number  of  hybrid  forms.  For  instance,  Professor 
Kerner  has  found  no  less  than  twenty-five  such  forms 
in  the  Alps.*  The  frequent  occurrence  of  hybrids  in 
this  genus  no  doubt  has  been  favoured  by  most  of  the 
species  being  heterostyled,  and  consequently  requiring 
cross-fertilisation  by  insects ;  yet  in  some  other  genera, 
species  which  are  not  heterostyled  and  which  in  some 
respects  appear  not  well  adapted  for  hybrid-ferti- 
lisation, have  likewise  been  largely  hybridised.  In 
certain  districts  of  England,  the  common  oxlip — a 
hybrid  between  the  cowslip  (P.  veris,  vel  officinalis)  and 
the  primrose  (P.  vulgaris,  vel  acaulis) — is  frequently 
found,  and  it  occurs  occasionally  almost  everywhere. 


*"DiePrimulaceen-Bastarten,"  'Bull.  Soc.  Bot.de  France,'  torn. 

'Oesterr.    Bot.    Zeitschrift,'    Jahr  x.,   1853,  p.  178.     Also  in  'Revue 

1875,   Nos.  3,  4,  and  5.     See  also  des  Sciences  Nat.,'  1875,  p.  331. 
Godron    on  hybrid    Primulas    in 


56  HYBRID  PRIMULAS.  CHAP.  II. 

Owing  to  the  frequency  of  this  intermediate  hybrid 
form,  and  to  the  existence  of  the  Bardfield  oxlip 
(P.  elatior),  which  resembles  to  a  certain  extent  the 
common  oxlip,  the  claim  of  the  three  forms  to  rank 
as  distinct  species  has  been  discussed  oftener  and  at 
greater  length  than  that  of  almost  any  other  plant. 
Linnaeus  considered  P.  veris,  vulgaris,  and  elatior  to  be 
varieties  of  the  same  species,  as  do  some  distinguished 
botanists  at  the  present  day;  whilst  others  who  have 
carefully  studied  these  plants  do  not  doubt  that  they 
are  distinct  species.  The  following  observations  prove, 
I  think,  that  the  latter  view  is  correct;  and  they  fur- 
ther show  that  the  common  oxlip  is  a  hybrid  between 
P.  veris  and  vulgaris. 

The  cowslip  differs  so  conspicuously  in  general  ap- 
pearance from  the  primrose,  that  nothing  need  here 
be  said  with  respect  to  their  external  characters.* 
But  some  less  obvious  differences  deserve  notice.  As 
both  species  are  heterostyled,  their  complete  fertili- 
sation depends  on  insects.  The  cowslip  is  habitually 
visited  during  the  day  by  the  larger  humble-bees 
(viz.  Bombus  muscorum  and  hortorum),  and  at  night 
by  moths,  as  I  have  seen  in  the  case  of  Cucullia.  The 
primrose  is  never  visited  (and  I  speak  after  many 
years'  observation)  by  the  larger  humble-bees,  and 
only  rarely  by  the  smaller  kinds;  hence  its  ferti- 
lisation must  depend  almost  exclusively  on  moths. 
There  is  nothing  in  the  structure  of  the  flowers  of  the 
two  plants  which  can  determine  the  visits  of  such 
widely  different  insects.  But  they  emit  a  different 
odour,  and  perhaps  their  nectar  may  have  a  different 
taste.  Both  the  long-styled  and  short-styled  forms  of 


*  The  Rev.  W.  A.  Leighton  seed,  in  '  Ann.  and  Mag.  of  Nat. 
has  pointed  out  certain  differences  Hist.,'  2nd  series,  vol.  ii.,  1848,  p. 
in  the  form  of  the  capsules  and  164. 


CHAP.  II.  THE  COMMON  OXLIP.  57 

the  primrose,  when  legitimately  and  naturally  ferti- 
lised, yield  on  an  average  many  more  seeds  per  capsule 
than  the  cowslip,  namely,  in  the  proportion  of  100  to 
55.  When  illegitimately  fertilised  they  are  likewise 
more  fertile  than  the  two  forms  of  the  cowslip,  as  shown 
by  the  larger  proportion  of  their  flowers  which  set  cap- 
sules, and  by  the  larger  average  number  of  seeds  which 
the  capsules  contain.  The  difference  also  between  the 
number  of  seeds  produced  by  the  long-styled  and  short- 
styled  flowers  of  the  primrose,  when  both  are  illegiti- 
mately fertilised,  is  greater  than  that  between  the  num- 
ber produced  under  similar  circumstances  by  the 
two  forms  of  the  cowslip.  The  long-styled  flowers  of 
the  primrose  when  protected  from  the  access  of  all  in- 
sects, except  such  minute  ones  as  Thrips,  yield  a  con- 
siderable number  of  capsules  containing  on  an  average 
19.2  seeds  per  capsule;  whereas  18  plants  of  the  long- 
styled  cowslip  similarly  treated  did  not  yield  a  single 
seed. 

The  primrose,  as  every  one  knows,  flowers  a  little, 
earlier  in  the  spring  than  the  cowslip,  and  inhabits 
slightly  different  stations  and  districts.  The  primrose 
generally  grows  on  banks  or  in  woods,  whilst  the  cow- 
slip is  found  in  more  open  places.  The  geographical 
range  of  the  two  forms  is  different.  Dr.  Bromfield  re- 
marks *  that  "  the  primrose  is  absent  from  all  the  in- 
terior region  of  northern  Europe,  where  the  cowslip  is 
indigenous."  In  Norway,  however,  both  plants  range 
to  the  same  degree  of  north  latitude,  f 

The  cowslip  and  primrose,  when  intercrossed,  be- 


* 'Phytologist.' vol.  iii.,  p.  694.  la  France,'  1840,  torn.   ii.  p.  376. 

t  H.  Lecoq,  '  Geograph.  Bot.  de  With  respect  to  the  rarity  of  P. 

1'Europe,'  torn,  viii.,  1858,  pp.  141,  veria    in    western    Scotland,    see 

144.     See  also  '  Ann.  and  Mag.  of  H.   C.   Watson,    '  Cybele    Britan- 

Nat.  Hist,,'  ix.,  1842,  pp.  156,  515.  nica,'  ii.  p.  293. 
Also  Boreau,   '  Flore  du  centre  de 
6 


58  HYBRID  PRIMULAS.  CHAP.  II. 

have  like  distinct  species,  for  they  are  far  from 
being  mutually  fertile.  Gartner  *  crossed  27  flowers 
of  P.  vulgaris  with  pollen  of  P.  veris,  and  obtained 
19  capsules;  but  these  did  not  contain  any  good 
seed.  He  also  crossed  21  flowers  of  P.  veris  with 
pollen  of  P.  vulgaris;  and  now  he  got  only  five 
capsules,  containing  seed  in  a  still  less  perfect 
condition.  Gartner  knew  nothing  about  hetero- 
stylism;  and  his  complete  failure  may  perhaps  be 
accounted  for  by  his  having  crossed  together  the 
same  forms  of  the  cowslip  and  primrose;  for  such 
crosses  would  have  been  of  an  illegitimate  as  well  as 
of  a  hybrid  nature,  and  this  would  have  increased 
their  sterility.  My  trials  were  rather  more  fortunate. 
Twenty-one  flowers,  consisting  of  both  forms  of  the 
cowslip  and  primrose,  were  intercrossed  legitimately, 
and  yielded  seven  capsules  (i.  e.  33  per  cent.),  contain- 
ing on  an  average  42  seeds;  some  of  these  seeds, 
however,  were  so  poor  that  they  probably  would  not  have 
germinated.  Twenty-one  flowers  on  the  same  cowslip 
and  primrose  plants  were  also  intercrossed  illegiti- 
mately, and  they  likewise  yielded  seven  capsules  (or 
33  per  cent.),  but  these  contained  on  an  average  only 
13  good  and  bad  seeds.  I  should,  however,  state  that 
some  of  the  above  flowers  of  the  primrose  were  fertilised 
with  pollen  from  the  polyanthus,  which  is  certainly  a 
variety  of  the  cowslip,  as  may  be  inferred  from  the  per- 
fect fertility  inter  se  of  the  crossed  offspring  from  these 
two  plants,  f  To  show  how  sterile  these  hybrid  unions 


*  'Bastarderzeugung,'  1849,  p.  ciently  numerous.  The  degree  of 

721-  infertility  of  a  cross  is  liable  to 

TMr.  Scott  has  discussed  the  much  fluctuation.  Pollen  from 
nature  of  the  polyanthus  CProc.  the  cowslip  at  first  appears  rather 
Linn.  Soc.  Bot.,'  viii.,  1864,  p.  more  efficient  on  the  primrose  than 
103),  and  arrives  at  a  different  that  of  the  polyanthus;  for  12 
conclusion ;  but  I  do  not  think  flowers  of  both  forms  of  the  prim- 
that  his  experiments  were  sum-  rose,  fertilised  legitimately  and 


CHAP.  II.  THE  COMMON  OXLIP.  59 

were,  I  may  remind  the  reader  that  90  per  cent,  of  the 
flowers  of  the  primrose  fertilised  legitimately  with 
primrose-pollen  yielded  capsules,  containing  on  an 
average  66  seeds;  and  that  54  per  cent,  of  the  flowers 
fertilised  illegitimately  yielded  capsules  containing  on 
an  average  3.55  seeds  per  capsule.  The  primrose, 
especially  the  short-styled  form,  when  fertilised  by  the 
cowslip,  is  less  sterile,  as  Gartner  likewise  observed, 
than  is  the  cowslip  when  fertilised  by  the  primrose. 
The  above  experiments  also  show  that  a  cross  between 
the  same  forms  of  the  primrose  and  cowslip  is  much 
more  sterile  than  that  between  different  forms  of  these 
two  species. 

The  seeds  from  the  several  foregoing  crosses  were 
sown,  but  none  germinated  except  those  from  the 
short-styled  primrose  fertilised  with  pollen  of  the 
polyanthus;  and  these  seeds  were  the  finest  of  the 
whole  lot.  I  thus  raised  six  plants,  and  compared  them 
with  a  group  of  wild  oxlips  which  I  had  trans- 
planted into  my  garden.  One  of  these  wild  oxlips 
produced  slightly  larger  flowers  than  the  others,  and 
this  one  was  identical  in  every  character  (in  foliage, 
flower-peduncle,  and  flowers)  with  my  six  plants, 
excepting  that  the  flowers  of  the  latter  were  tinged  of 
a  dingy  red  colour,  from  being  descended  from  the 
polyanthus. 

We  thus  see  that  the  cowslip  and  primrose  can- 
not be  crossed  either  way  except  with  considerable 
difficulty,  that  they  differ  conspicuously  in  external 
appearance,  that  they  differ  in  various  physiological 


illegitimately  with  pollen  of  the  22.6  seeds.  On  the  other  hand, 
cowslip  gave  five  capsules,  contain-  the  seeds  produced  by  the  poly- 
ing  on  an  average  32.4  seeds ;  anthus-pollen  were  much  the  fin- 
whilst  18  flowers  similarly  ferti-  est  of  the  whole  lot,  and  were  the 
lised  by  polyanthus-pollen  yielded  only  ones  which  germinated, 
only  five  capsules,  containing  only 


60  HYBRID  PRIMULAS.  CHAP.  II. 

characters,  that  they  inhabit  slightly  different  stations 
and  range  differently.  Hence  those  botanists  who 
rank  these  plants  as  varieties  ought  to  be  able  to  prove 
that  they  are  not  as  well  fixed  in  character  as  are  most 
species;  and  the  evidence  in  favour  of  such  instability 
of  character  appears  at  first  sight  very  strong.  It 
rests,  first,  on  statements  made  by  several  competent 
observers  that  they  have  raised  cowslips,  primroses,  and 
oxlips  from  seeds  of  the  same  plant;  and,  secondly, 
on  the  frequent  occurrence  in  the  state  of  nature  of 
plants  presenting  every  intermediate  gradation  between 
the  cowslip  and  primrose. 

The  first  statement,  however,  is  of  little  value; 
for,  heterostylism  not  being  formerly  understood, 
the  seed-bearing  plants  were  in  no  instance  *  pro- 
tected from  the  visits  of  insects;  and  there  would 
be  almost  as  much  risk  t)f  an  isolated  cowslip,  or  of 
several  cowslips  if  consisting  of  the  same  form,  being 
crossed  by  a  neighbouring  primrose  and  producing  ox- 
lips,  as  of  one  sex  of  a  dioecious  plant,  under  similar 
circumstances,  being  crossed  by  the  opposite  sex  of 
an  allied  and  neighbouring  species.  Mr.  H.  C.  Wat- 
son, a  critical  and  most  careful  observer,  made  many 
experiments  by  sowing  the  seeds  of  cowslips  and  of 
various  kinds  of  oxlips,  and  arrived  at  the  following 
conclusion,!  namely,  "  that  seeds  of  the  cowslip  can 
produce  cowslips  and  oxlips,  and  that  seeds  of  an  oxlip 
can  produce  cowslips,  oxlips,  and  primroses."  This 
conclusion  harmonises  perfectly  with  the  view  that  in 


*  One  author  states  in  the  '  Phy-  tained  an  abundance  of  seed, 
tologist'  (vol.  iii.  p.  703)  that  he  which  is  simply  impossible, 
covered  with  bell-glasses  some  cow-  Hence  there  must  have  been 
slips,  primroses,  &c.,  on  which  he  some  strange  error  in  these  ex- 
experimented.  He  specifies  all  periments.  which  may  be  passed 
the  details  of  his  experiment,  but  over  as  valueless, 
does  not  say  that  he  artificially  f  'Phytologist,'  ii.  pp.  217,  852; 
fertilised  his  plants ;  yet  he  ob-  iii.  p.  43. 


CHAP.  II.  THE  COMMON  OXLIP.  61 

all  cases,  when  such  results  have  been  obtained,  the 
unprotected  cowslips  have  been  crossed  by  primroses, 
and  the  unprotected  oxlips  by  either  cowslips  or 
primroses;  for  in  this  latter  case  we  might  expect,  by 
the  aid  of  reversion,  which  notoriously  comes  into 
powerful  action  with  hybrids,  that  the  two  parent-forms 
in  appearance  pure,  as  well  as  many  intermediate  grada- 
tions, would  be  occasionally  produced.  Nevertheless 
the  two  following  statements  offer  considerable  diffi- 
culty. The  Rev.  Prof.  Henslow  *  raised  from  seeds  of  a 
cowslip  growing  in  his  garden,  various  kinds  of  oxlips 
and  one  perfect  primrose ;  but  a  statement  in  the  same 
paper  perhaps  throws  light  on  this  anomalous  result. 
Prof.  Henslow  had  previously  transplanted  into  his 
garden  a  cowslip,  which  completely  changed  its  ap- 
pearance during  the  following  year,  and  now  resembled 
an  oxlip.  Next  year  again  it  changed  its  character, 
and  produced,  in  addition  to  the  ordinary  umbels,  a 
few  single-flowered  scapes,  bearing  flowers  somewhat 
smaller  and  more  deeply  coloured  than  those  of  the 
common  primrose.  From  what  I  have  myself  observed 
with  oxlips,  I  cannot  doubt  that  this  plant  was  an  ox- 
lip  in  a  highly  variable  condition,  almost  like  that  of 
the  famous  Cytisus  adami.  This  presumed  oxlip  was 
propagated  by  offsets,  which  were  planted  in  different 
parts  of  the  garden;  and  if  Prof.  Henslow  took  by 
mistake  seeds  from  one  of  these  plants,  especially  if  it 
had  been  crossed  by  a  primrose,  the  result  would  be 
quite  intelligible.  Another  case  is  still  more  difficult 
to  understand :  Dr.  Herbert  f  raised,  from  the  seeds  of 
a  highly  cultivated  red  cowslip,  cowslips,  oxlips  of 
various  kinds,  and  a  primrose.  This  case,  if  accurately 


*  London's 'Mag.  of  Nat.  Hist.,'        t  'Transact.  Hort.  Soc.,'  iv.  p. 
iii.  1830,  p.  409.  19. 


62  HYBRID  PRIMULAS.  CHAP.  H. 

recorded,  which  I  must  doubt,  is  explicable  only  on 
the  improbable  assumption  that  the  red  cowslip  was 
not  of  pure  parentage.  With  species  and  varieties 
of  many  kinds,  when  intercrossed,  one  is  sometimes 
strongly  prepotent  over  the  other;  and  instances  are 
known*  of  a  variety,  crossed  by  another,  producing 
offspring  which  in  certain  characters,  as  in  colour, 
hairiness,  &c.,  have  proved  identical  with  the  pollen- 
bearing  parent,  and  quite  dissimilar  to  the  mother- 
plant;  but  I  do  not  know  of  any  instance  of  the  off- 
spring of  a  cross  perfectly  resembling,  in  a  consider- 
able number  of  important  characters,  the  father  alone. 
It  is,  therefore,  very  improbable  that  a  pure  cowslip 
crossed  by  a  primrose  should  ever  produce  a  primrose 
in  appearance  pure.  Although  the  facts  given  by  Dr. 
Herbert  and  Prof.  Henslow  are  difficult  to  explain,  yet 
until  it  can  be  shown  that  a  cowslip  or  a  primrose, 
carefully  protected  from  insects,  will  give  birth  to  at 
least  oxlips,  the  cases  hitherto  recorded  have  little  weight 
in  leading  us  to  admit  that  the  cowslip  and  primrose 
are  varieties  of  one  and  the  same  species. 

Negative  evidence  is  of  little  value;  but  the  follow- 
ing facts  may  be  worth  giving: — Some  cowslips  which 
had  been  transplanted  from  the  fields  into  a  shrubbery 
were  again  transplanted  into  highly  manured  land.  In 
the  following  year  they  were  protected  from  insects, 
artificially  fertilised,  and  the  seed  thus  procured  was 
sown  in  a  hotbed.  'The  young  plants  were  afterwards 
planted  out,  some  in  very  rich  soil,  some  in  stiff  poor 
clay,  some  in  old  peat,  and  some  in  pots  in  the  green- 
house; so  that  these  plants,  765  in  number,  as  well  as 
their  parents,  were  subjected  to  diversified  and  un- 


*  I  have  given  instances  in  my    cation,'  ch.  xv.  2nd  edit.  vol.  ii. 
work   'On  the  Varintion  of  Ani-    p.  69. 
mals  and  Plants  under  Domesti- 


CHAP.  II.  THE  COMMON  OXLIP.  63 

natural  treatment;  but  not  one  of  them  presented  the 
least  variations  except  in  size — those  in  the  peat  at- 
taining almost  gigantic  dimensions,  and  those  in  the 
clay  being  much  dwarfed. 

I  do  not,  of  course,  doubt  that  cowslips  exposed 
during  several  successive  generations  to  changed  con- 
ditions would  vary,  and  that  this  might  occasionally 
occur  in  a  state  of  nature.  Moreover,  from  the  law 
of  analogical  variation,  the  varieties  of  any  one  species 
of  Primula  would  probably  in  some  cases  resemble 
other  species  of  the  genus.  For  instance,  I  raised  a  red 
primrose  from  seed  from  a  protected  plant,  and  the 
flowers,  though  still  resembling  those  of  the  primrose, 
were  borne  during  one  season  in  umbrels  on  a  long  foot- 
stalk like  that  of  a  cowslip. 

With  regard  to  the  second  class  of  facts  in  support 
of  the  cowslip  and  primrose  being  ranked  as  mere 
varieties,  namely,  the  well-ascertained  existence  in  a 
state  of  nature  of  numerous  linking  forms* : — If  it  can 
be  shown  that  the  common  wild  oxlip,  which  is  inter- 
mediate in  character  between  the  cowslip  and  prim- 
rose, resembles  in  sterility  and  other  essential  respects 
a  hybrid  plant,  and  if  it  can  further  be  shown  that  the 
oxlip,  though  in  a  high  degree  sterile,  can  be  fertilised 
by  either  parent-species,  thus  giving  rise  to  still  finer 
gradational  links,  then  the  presence  of  such  linking 
forms  in  a  state  of  nature  ceases  to  be  an  argument 
of  any  weight  in  favour  of  the  cowslip  and  primrose 
being  varieties,  and  becomes,  in  fact,  an  argument  on 
the  other  side.  The  hybrid  origin  of  a  plant  in  a 
state  of  nature  can  be  recognised  by  four  tests:  first, 
by  its  occurrence  only  where  both  presumed  parent- 


*See  an    excellent   article    on    in  the  'Phytologist,'   vol.  iii.  p. 
this  subject  by  Mr.  H.  C.  Watson,    43. 


64:  HYBRID  PRIMULAS.  CHAP.  II. 

species  exist  or  have  recently  existed;  and  this  holds 
good,  as  far  as  I  can  discover,  with  the  oxlip;  but  the 
P.  elatior  of  Jacq.,  which,  as  we  shall  presently  see, 
constitutes  a  distinct  species,  must  not  be  confounded 
with  the  common  oxlip.  Secondly,  by  the  supposed 
hybrid  plant  being  nearly  intermediate  in  character 
between  the  two  parent-species,  and  especially  by  its 
resembling  hybrids  artificially  made  between  the  same 
two  species.  Now  the  oxlip  is  intermediate  in  char- 
acter, and  resembles  in  every  respect,  except  in  the 
colour  of  the  corolla,  hybrids  artificially  produced  be- 
tween the  primrose  and  the  polyanthus,  which  latter 
is  a  variety  of  the  cowslip.  Thirdly,  by  the  supposed 
hybrids  being  more  or  less  sterile  when  crossed  inter 
se :  but  to  try  this  fairly,  two  distinct  plants  of  the  same 
parentage,  and  not  two  flowers  on  the  same  plant, 
should  be  crossed;  for  many  pure  species  are  more 
or  less  sterile  with  pollen  from  the  same  individual 
plant;  and  in  the  case  of  hybrids  from  heterostyled 
species  the  opposite  forms  should  be  crossed.  Fourthly 
and  lastly,  by  the  supposed  hybrids  being  much  more 
fertile  when  crossed  with  either  pure  parent-species  than 
when  crossed  inter  se,  but  still  not  as  fully  fertile  as 
the  parent-species. 

For  the  sake  of  ascertaining  the  two  latter  points, 
I  transplanted  a  group  of  wild  oxlips  into  my 
garden.  They  consisted  of  one  long-styled  and 
three  short-styled  plants,  which,  except  in  the  co- 
rolla of  one  being  slightly  larger,  resembled  each 
other  closely.  The  trials  which  were  made,  and  the 
results  obtained,  are  shown  in  the  five  following 
tables.  No  less  than  twenty  different  crosses  are 
necessary  in  order  to  ascertain  fully  the  fertility  of 
hybrid  heterostyled  plants,  both  inter  se  and  with 
their  two  parent-species.  In  this  instance  256  flowers 


CHAP.  II. 


THE  COMMON  OXLIP. 


65 


were  crossed  in  the  course  of  four  seasons.  I  may 
mention,  as  a  mere  curiosity,  that  if  any  one  were  to 
raise  hybrids  between  two  trimorphic  heterostyled 
species,  he  would  have  to  make  90  distinct  unions  in 
order  to  ascertain  their  fertility  in  all  ways;  and  as  he 
would  have  to  try  at  least  10  flowers  in  each  case,  he 
would  be  compelled  to  fertilise  900  flowers  and  count 
their  seeds.  This  would  probably  exhaust  the  patience 
of  the  most  patient  man. 


TABLE  14. 

Crosses  inter  se  between  the  two  forms  of  the  common 
Oxlip. 


Illegitimate  union. 

Legitimate  union. 

Illegitimate  union. 

Legitimate  union. 

Short-styled  ox- 
lip,  by  pollen  of 
short-styled    ox- 
lip:  20  flowers  fer- 

Short-styled ox- 
lip,  by  pollen  of 
long-styled  oxlip: 
10  flowers  ferti- 

Long-styled ox- 
lip,   by   its    own 
pollen  :  24  flowers 
fertilised,       pro- 

Long-styled ox- 
lip,  by  pollen  of 
short-styled     ox- 
lip:     10    flowers 

tilised,    did    not 

lised,  did  not  pro- 

duced   five    cap- 

fertilised, did  not 

produce  one  cap- 

duce one  capsule. 

sules,  containing 

produce  one  cap- 

sule. 

6,  10,  20,  8,  and  14 

sule. 

seeds.       Average 

11.6. 

TABLE  15. 

Both  forms  of  the  Oxlip  crossed  with  Pollen  of  both 
forms  of  the  Cowslip,  P.  veris. 


Illegitimate  union. 

Legitimate  union. 

Illegitimate  union. 

Legitimate  union. 

Short-styled  ox- 
lip,  by  pollen  of 

Short-styled  ox- 
lip,  by  pollen  of 

Long-styled  ox- 
lip,  by  pollen  of 

Long-styled  ox- 
lip,  by  pollen  of 

short-styled  cow- 

long-styled  cow- 

long-styled  cow- 

short-styled cow- 

slip :    18    flowers 

slip:  ISflowcrsfer- 

slip  :    11    flowers 

slip:  5  flowers  fer- 

fertilised, did  not 

tilised,  produced 

fertilised,       pro- 

tilised, produced 

produce  one  cap- 
sule. 

three      capsules, 
containing    7,   3, 

duced    one    cap- 
sule,    containing 

two  capsules,  con- 
taining 21  and  28 

and    3   wretched 

ISwretched  seeds. 

very  fine  seeds. 

seeds,  apparently 

incapable  of  ger- 

mination. 

66 


HYBRID  PRIMULAS. 


CHAP.  II. 


TABLE  16. 

Both  forms  of  the  Oxlip  crossed  with  Pollen  of  both 
forms  of  the  Primrose,  P.  vulgaris. 


Illegitimate  union. 

Legitimate  union. 

Illegitimate  union- 

Legitimate  union. 

Short-styled  ox- 
lip,  by  pollen  of 
s  h  o  r  t  -  s  t  y  1  e  d 

Short-styled  ox- 
lip,  by  pollen  of 
long-styled  prim- 

Long-styled ox- 
lip,  by  pollen  of 
long-styled  prim- 

Long-styled ox- 
lip,  by  pollen  of 
short-styled 

primrose:  34  flow- 

rose :   26  flowers 

rose  :    11  flowers 

primrose:  5  flow- 

ers fertilised,  pro- 

fertilised,      pro- 

fertilised,      pro- 

ers fertilised,  pro- 

duced   two    cap- 

duced   six    cap- 

duced   four  cap- 

duced   five    cap- 

sules, containing 
5  and  12  seeds. 

sules,  containing 
16,  20,  5,  10,  19, 
and  24  seeds.  Av- 

sules, containing 
10,   7,  5,    and    6 
wretched    seeds. 

sules,  containing 
26,  32,  23,  28,  and 
34  seeds.  Average 

erage  15.7.  Many 

Average  7.0. 

28.6. 

of  the  seeds  very 

poor,  some  good. 

TABLE  17. 

Both  forms  of  the  Cowslip  crossed  with  Pollen  of 

both  forms  of  the  Oxlip. 

Illegitimate  union. 

Legitimate  union. 

Illegitimate  union. 

Legitimate  union. 

Short-styled 
cowslip,   by   pol- 
len of  short-styled 
oxlip:    8  flowers 
fertilised,       pro- 

Long- styled 
cowslip,  by    pol- 
len of  short-styled 
oxlip:    8  flowers 
fertilised,       pro- 

Long- styled 
cowslip,  by   pol- 
len of  long-styled 
oxlip  :   8  flowers 
fertilised,       pro- 

Short- styled 
cowslip,   by  pol- 
len of  long-styled 
oxlip  :    8  flowers 
fertilised,       pro- 

duced    not    one 

duced    one    cap- 

duced three  cap- 

duced eight  cap- 

capsule. 

sule,    containing 

sules,  containing 

sules,  containing 

26  seeds. 

5,  6,  and  14  seeds. 

58,  38,  31,  44,  23, 

Average  8.3. 

26,     37,    and    66 

seeds.      Average 

40.4. 

TABLE  18. 

Both  forms  of  the  Primrose  crossed  with  Pollen  of 
both  forms  of  the  Oxlip. 


Illegitimate  union. 

Legitimate  union. 

Illegitimate  union. 

Legitimate  union. 

Short-  styled 

Long-  styled 

Long-  styled 

Short-  styled 

primrose,  by  pol- 
len ofshort-styled 
oxlip:    8   flowers 

primrose,  by  pol- 
len ofshort-styled 
oxlip  :    8  flowers 

primrose,  by  pol- 
len of  long-styled 
oxlip:    8   flowers 

primrose,  by  pol- 
len of  long-styled 
oxlip  :    8  flowers 

fertilised,       pro- 

fertilised,      pro- 

fertilised,      pro- 

fertilised,      pro- 

duced    not    one 

duced    two    cap- 

duced eight  cap- 

duced   four  cap- 

capsule. 

sules,  containing 

sules,  containing 

sules,  containing 

5  and  2  seeds. 

15,  7,  12,  20,  22,  7, 

52,  52,  42,  and  49 

16,  and  13  seeds. 

seeds,  some  good 

Average  14.0. 

and     some    bad. 

Average  48.7. 

CHAP.  II.  THE  COMMON  OXL1P.  67 

"We  see  in  these  five  tables  the  number  of  capsules 
and  of  seeds  produced,  by  crossing  both  forms  of  the 
oxl  ip  in  a  legitimate  and  illegitimate  manner  with  one 
another,  and  with  the  two  forms  of  the  primrose  and 
cowslip.  I  may  premise  that  the  pollen  of  two  of  the 
short-styled  oxlips  consisted  of  nothing  but  minute 
aborted  whitish  cells ;  but  in  the  third  short-styled  plant 
about  one  fifth  of  the  grains  appeared  in  a  sound  con- 
dition. Hence  it  is  not  surprising  that  neither  the 
short-styled  nor  the  long-styled  oxlip  produced  a  single 
seed  when  fertilised  with  this  pollen.  Nor  did  the 
pure  cowslips  or  primroses  when  illegitimately  ferti- 
lised with  it ;  but  when  thus  legitimately  fertilised  they 
yielded  a  few  good  seeds.  The  female  organs  of  the 
short-styled  oxlips,  though  greatly  deteriorated  in 
power,  were  in  rather  better  condition  than  the  male 
organs;  for  though  the  short-styled  oxlips  yielded  no 
seeds  when  fertilised  by  the  long-styled  oxlips,  and 
hardly  any  when  illegitimately  fertilised  by  pure 
cowslips  or  primroses,  yet  when  legitimately  fertilised 
by  these  latter  species,  especially  by  the  long-styled 
primrose,  they  yielded  a  moderate  supply  of  good 
seed. 

The  long-styled  oxlip  was  more  fertile  than  the 
three  short-styled  oxlips,  and  about  half  its  pollen- 
grains  appeared  sound.  It  bore  no  seed  when  legiti- 
mately fertilised  by  the  short-styled  oxlips;  but  this 
no  doubt  was  due  to  the  badness  of  the  pollen  of  the 
latter;  for  when  illegitimately  fertilised  (Table  14) 
by  its  own  pollen  it  produced  some  good  seeds, 
though  much  fewer  than  self-fertilised  cowslips  or 
primroses  would  have  produced.  The  long-styled  ox- 
lip  likewise  yielded  a  very  low  average  of  seed,  as  may 
be  seen  in  the  third  compartment  of  the  four  latter 
tables,  when  illegitimately  fertilised  by,  and  when 


68  HYBRID  PRIMULAS.  CHAP.  II. 

illegitimately  fertilising,  pure  cowslips  and  primroses. 
The  four  corresponding  legitimate  unions,  however, 
were  moderately  fertile,  and  one  (viz.  that  between  a 
short-styled  cowslip  and  the  long-styled  oxlip  in  Table 
17)  was  nearly  as  fertile  as  if  both  parents  had  been 
pure.  A  short-styled  primrose  legitimately  fertilised  by 
the  long-styled  oxlip  (Table  18)  also  yielded  a  moder- 
ately good  average,  namely  48.7  seeds;  but  if  this  short- 
styled  primrose  had  been  fertilised  by  a  long-styled 
primrose  it  would  have  yielded  an  average  of  65  seeds. 
If  we  take  the  ten  legitimate  unions  together,  and  the 
ten  illegitimate  unions  together,  we  shall  find  that  29 
per  cent,  of  the  flowers  fertilised  in  a  legitimate  man- 
ner yielded  capsules,  these  containing  on  an  average 
27.4  good  and  bad  seeds;  whilst  only  15  per  cent,  of 
the  flowers  fertilised  in  an  illegitimate  manner  yielded 
capsules,  these  containing  on  an  average  only  11.0  good 
and  bad  seeds. 

In  a  previous  part  of  this  chapter  it  was  shown  that 
illegitimate  crosses  between  the  long-styled  form  of 
the  primrose  and  the  long-styled  cowslip,  and  between 
the  short-styled  primrose  and  short-styled  cowslip,  are 
more  sterile  than  legitimate  crosses  between  these  two 
species;  and  we  now  see  that  the  same  rule  holds  good 
almost  invariably  with  their  hybrid  offspring,  whether 
these  are  crossed  inter  se,  or  with  either  parent-species, 
so  that  in  this  particular  case,  but  not  as  we  shall  pres- 
ently see  in  other  cases,  the  same  rule  prevails  with 
the  pure  unions  between  the  two  forms  of  the  same 
heterostyled  species,  with  crosses  between  two  distinct 
heterostyled  species,  and  with  their  hybrid  offspring. 

Seeds  from  the  long-styled  oxlip  fertilised  by  its 
own  pollen  were  sown,  and  three  long-styled  plants 
raised.  The  first  of  these  was  identical  in  every 
character  with  its  parent.  The  second  bore  rather 


CHAP.  II.  THE  COMMON  OXLIP.  69 

smaller  flowers,  of  a  paler  colour,  almost  like  those  of 
the  primrose;  the  scapes  were  at  first  single-flowered, 
but  later  in  the  season  a  tall  thick  scape,  bearing  many 
flowers,  like  that  of  the  parent  oxlip,  was  thrown  up. 
The  third  plant  likewise  produced  at  first  only  single- 
flowered  scapes,  with  the  flowers  rather  small  and  of 
a  darker  yellow;  but  it  perished  early.  The  second 
plant  also  died  in  September;  and  the  first  plant, 
though  all  three  grew  under  very  favourable  condi- 
tions, looked  very  sickly.  Hence  we  may  infer  that 
seedlings  from  self-fertilised  oxlips  would  hardly  be 
able  to  exist  in  a  state  of  nature.  I  was  surprised  to 
find  that  all  the  pollen-grains  in  the  first  of  these  seed- 
ling oxlips  appeared  sound;  and  in  the  second  only  a 
moderate  number  were  bad.  These  two  plants,  however, 
had  not  the  power  of  producing  a  proper  number  of 
seeds;  for  though  left  uncovered  and  surrounded  by 
pure  primroses  and  cowslips,  the  capsules  were  esti- 
mated to  include  an  average  of  only  from  fifteen  to 
twenty  seeds. 

From  having  many  experiments  in  hand,  I  did  not 
sow  the  seed  obtained  by  crossing  both  forms  of  the 
primrose  and  cowslip  with  both  forms  of  the  oxlip, 
which  I  now  regret;  but  I  ascertained  an  interest- 
ing point,  namely,  the  character  of  the  offspring 
from  oxlips  growing  in  a  state  of  nature  near  both 
primroses  and  cowslips.  The  oxlips  were  the  same 
plants  which,  after  their  seeds  had  been  collected,  were 
transplanted  and  experimented  on.  From  the  seeds 
thus  obtained  eight  plants  were  raised,  which,  when 
they  flowered,  might  have  been  mistaken  for  pure 
primroses;  but  on  close  comparison  the  eye  in  the 
centre  of  the  corolla  was  seen  to  be  of  a  darker  yellow 
and  the  peduncles  more  elongated.  As  the  season  ad- 
vanced, one  of  these  plants  threw  up  two  naked  scapes, 


70  HYBRID  PRIMULAS.  CHAP.  II. 

7  inches  in  height,  which  bore  umbels  of  flowers  of 
the  same  character  as  before.  This  fact  led  me  to  ex- 
amine the  other  plants  after  they  had  flowered  and 
were  dug  up;  and  I  found  that  the  flower-peduncles 
of  all  sprung  from  an  extremely  short  common  scape, 
of  which  no  trace  can  be  found  in  the  pure  primrose. 
Hence  these  plants  are  beautifully  intermediate  be- 
tween the  oxlip  and  the  primrose,  inclining  rather 
towards  the  latter ;  and  we  may  safely  conclude  that  the 
parent  oxlips  had  been  fertilised  by  the  surrounding 
primroses. 

From  the  various  facts  now  given,  there  can  be  no 
doubt  that  the  common  oxlip  is  a  hybrid  between  the 
cowslip  (P.  veris,  Brit.  Fl.)  and  the  primrose  (P.  vul- 
garis,  Brit.  FL),  as  has  been  surmised  by  several 
botanists.  It  is  probable  that  oxlips  may  be  produced 
either  from  the  cowslip  or  the  primrose  and  the  seed- 
bearer,  but  oftenest  from  the  latter,  as  I  judge  from 
the  nature  of  the  stations  in  which  oxlips  are  generally 
found,*  and  from  the  primrose  when  crossed  by  the 
cowslip  being  more  fertile  than,  conversely,  the  cowslip 
by  the  primrose.  The  hybrids  themselves  are  also 
rather  more  fertile  when  crossed  with  the  primrose 
than  with  the  cowslip.  Whichever  may  be  the  seed- 
bearing  plant,  the  cross  is  probably  between  different 
forms  of  the  two  species;  for  we  have  seen  that  legiti- 
mate hybrid  unions  are  more  fertile  than  illegitimate 
hybrid  unions.  Moreover  a  friend  in  Surrey  found 
that  29  oxlips  which  grew  in  the  neighbourhood  of 
his  house  consisted  of  13  long-styled  and  16  short- 
styled-plants ;  now,  if  the  parent-plants  had  been 
illegitimately  united,  either  the  long-  or  short-styled 
form  would  have  greatly  preponderated,  as  we  shall 


*  See  also  on  this  head  Hardwicke's  'Science-Gossip,'   1867,  pp. 
114,  137. 


CHAP.  II.  THE  COMMON  OXLIP.  ft 

hereafter  see  good  reason  to  believe.  The  case  of 
the  oxlip  is  interesting;  for  hardly  any  other  in- 
stance is  known  of  a  hybrid  spontaneously  arising  in 
such  large  numbers  over  so  wide  an  extent  of  coun- 
try. The  common  oxlip  (not  the  P.  elatior  of  Jacq.)  is 
found  almost  everywhere  throughout  England,  where 
both  cowslips  and  primroses  grow.  In  some  districts, 
as  I  have  seen  near  Hartfield  in  Sussex  and  in  parts 
of  Surrey,  specimens  may  be  found  on  the  borders  of 
almost  every  field  and  small  wood.  In  other  districts 
the  oxlip  is  comparatively  rare:  near  my  own  resi- 
dence I  have  found,  during  the  last  twenty-five  years, 
not  more  than  five  or  six  plants  or  groups  of  plants. 
It  is  difficult  to  conjecture  what  is  the  cause  of  this 
difference  in  their  number.  It  is  almost  necessary 
that  a  plant,  or  several  plants,  belonging  to  the  same 
form,  of  one  parent-species,  should  grow  near  the 
opposite  form  of  the  other  parent-species;  and  it  is 
further  necessary  that  both  species  should  be  frequented 
by  the  same  kind  of  insect,  no  doubt  a  moth.  The 
cause  of  the  rare  appearance  of  the  oxlip  in  certain 
districts  may  be  the  rarity  of  some  moth,  which  in 
other  districts  habitually  visits  both  the  primrose  and 
cowslip. 

Finally,  as  the  cowslip  and  primrose  differ  in  the 
various  characters  above  specified, — as  they  are  in  a 
high  degree  sterile  when  intercrossed, — as  there  is  no 
trustworthy  evidence  that  either  species,  when  un- 
crossed, has  ever  given  birth  to  the  other  species  or 
to  any  intermediate  form, — and  as  the  intermediate 
forms  which  are  often  found  in  a  state  of  nature  have 
been  shown  to  be  more  or  less  sterile  hybrids  of  the 
first  or  second  generation, — we  must  for  the  future 
look  at  the  cowslip  and  primrose  as  good  and  true 
species. 


Y2  THE  BARDFIELD  OXLIP.  CHAP.  II. 

Primula  elatior,  Jacq.,  or  the  Bardfield  Oxlip,  is 
found  in  England  only  in  two  or  three  of  the  eastern 
counties.  On  the  Continent  it  has  a  somewhat  dif- 
ferent range  from  that  of  the  cowslip  and  primrose; 
and  it  inhabits  some  districts  where  neither  of  these 
species  live.*  In  general  appearance  it  differs  so  much 
from  the  common  oxlip,  that  no  one  accustomed  to 
see  both  forms  in  the  living  state  could  afterwards 
confound  them;  but  there  is  scarcely  more  than  a 
single  character  by  which  they  can  be  distinctly  de- 
fined, namely,  their  linear-oblong  capsules  equalling  the 
calyx  in  length,  f  The  capsules  when  mature  differ 
conspicuously,  owing  to  their  length,  from  those  of  the 
cowslip  and  primrose.  .  With  respect  to  the  fertility 
of  the  two  forms  when  these  are  united  in  the  four 
possible  methods,  they  behave  like  the  other  hetero- 
styled  species  of  the  genus,  but  differ  somewhat  (see 
Table  8  and  12)  in  the  smaller  proportion  of  the  illegi- 
timately fertilised  flowers  which  set  capsules.  That 
P.  elatior  is  not  a  hybrid  is  certain,  for  when  the  two 
forms  were  legitimately  united  they  yielded  the  large 
average  of  47.1  seeds,  and  when  illegitimately  united 
35.5  per  capsule;  whereas,  of  the  four  possible  unions 
(Table  14)  between  the  two  forms  of  the  common  ox- 
lip  which  we  know  to  be  a  hybrid,  one  alone  yielded 
any  seed;  and  in  this  case  the  average  number  was 
only  11.6  per  capsule.  Moreover  I  could  not  detect 
a  single  bad  pollen-grain  in  the  anthers  of  the  short- 
styled  P.  elatior;  whilst  in  two  short-styled  plants  of 
the  common  oxlip  all  the  grains  were  bad,  as  were 
a  large  majority  in  a  third  plant.  As  the  common 


*  For  England,  see  Hewett  C.  1858,   p.   142.     For  the  Alps,   see 

Watson,  'Cybele  Britannica,' vol.  'Ann.  and  Mag.  Nat.  Hist.,' vol. 

ii.,  1849,  p.   292.      For  the  Con-  ix.,  1842,  pp.  156  and  515. 

tinent,    see     Lecoq,     '  Geograph.  f  Babington's  '  Manual  of  Brit- 

Botaniquede  1'Europe,'  torn,  viii.,  ish  Botany,'  1851,  p.  258. 


CHAP.  II.  THE  BARDFIELD  OXLIP.  73 

oxlip  is  a  hybrid  between  the  primrose  and  cowslip,  it 
is  not  surprising  that  eight  long-styled  flowers  of  the 
primrose,  fertilised  by  pollen  from  the  long-styled 
common  oxlip,  produced  eight  capsules  (Table  18), 
containing,  however,  only  a  low  average  of  seeds; 
whilst  the  same  number  of  flowers  of  the  primrose, 
similarly  fertilised  by  the  long-styled  Bardfield  oxlip, 
produced  only  a  single  capsule;  this  latter  plant 
being  an  altogether  distinct  species  from  the  primrose. 
Plants  of  P.  elatior  have  been  propagated  by  seed  in 
a  garden  for  twenty-five  years,  and  have  kept  all  this 
time  quite  constant,  excepting  that  in  some  cases  the 
flowers  varied  a  little  in  size  and  tint.*  Nevertheless, 
according  to  Mr.  H.  C.  Watson  and  Dr.  Bromfield,f 
plants  may  be  occasionally  found  in  a  state  of  nature, 
in  which  most  of  the  characters  by  which  this  species 
can  be  distinguished  from  P.  veris  and  vulgaris  fail; 
but  such  intermediate  forms  are  probably  due  to  hybridi- 
sation; for  Kerner  states  in  the  paper  before  referred 
to,  that  hybrids  sometimes,  though  rarely,  arise  in  the 
Alps  between  P.  elatior  and  veris. 

Finally,  although  we  may  freely  admit  that  Primula 
veris,  vulgaris,  and  elatior,  as  well  as  all  the  other 
species  of  the  genus,  are  descended  from  a  common 
primordial  form,  yet  from  the  facts  above  given,  we 
must  conclude  that  these  three  forms  are  now  as  fixed 
in  character  as  are  many  others  which  are  universally 
ranked  as  true  species.  Consequently  they  have  as 
good  a  right  to  receive  distinct  specific  names  as  have, 
for  instance,  the  ass,  quagga,  and  zebra. 

Mr.  Scott  has  arrived  at  some  interesting  results  by 

*  See  Mr.  H.  Doubleday  in  the  '  Gardener's  Chronicle,'  1867,  p.  435  ; 
also  Mr.  W.  Marshall,  ibid.,  p.  462. 

t  'Phytologist,'  vol.  i.  p.  1001,  and  vol.  iii.  p.  695. 


74  HYBRID  PRIMULAS.  CHAP.  II. 

crossing  other  heterostyled  species  of  Primula.*  I 
have  already  alluded  to  his  statement,  that  in  four  in- 
stances (not  to  mention  others)  a  species  when  crossed 
with  a  distinct  one  yielded  a  larger  number  of  seeds 
than  the  same  species  fertilised  illegitimately  with  its 
own-form  pollen,  though  taken  from  a  distinct  plant. 
It  has  long  been  known  from  the  researches  of  Kolreuter 
and  Gartner,  that  two  species  when  crossed  reciprocally 
sometimes  differ  as  widely  as  is  possible  in  their  fer- 
tility: thus  A  when  crossed  with  the  pollen  of  B  will 
yield  a  large  number  of  seeds,  whilst  B  may  be  crossed 
repeatedly  with  pollen  of  A,  and  will  never  yield  a  single 
seed.  Now  Mr.  Scott  shows  in  several  cases  that  the 
same  law  holds  good  when  two  heterostyled  species 
of  Primula  are  intercrossed,  or  when  one  is  crossed 
with  a  homostyled  species.  But  the  results  are  much 
more  complicated  than  with  ordinary  plants,  as  two 
heterostyled  dimorphic  species  can  be  intercrossed  in 
eight  different  ways.  I  will  give  one  instance  from 
Mr.  Scott.  The  long-styled  P.  hirsuta  fertilised  legit- 
imately and  illegitimately  with  pollen  from  the  two 
forms  of  P.  auricula,  and  reciprocally  the  long-styled 
P.  auricula  fertilised  legitimately  and  illegitimately 
with  pollen  from  the  two  forms  of  P.  hirsuta,  did 
not  produce  a  single  seed.  Nor  did  the  short- 
styled  P.  hirsuta  when  fertilised  legitimately  and 
illegitimately  with  the  pollen  of  the  two  forms  of 
P.  auricula.  On  the  other  hand,  the  short-styled  P. 
auricula  fertilised  with  pollen  from  the  long-styled 
P.  hirsuta  yielded  capsules  containing  on  an  average 
no  less  than  56  seeds;  and  the  short-styled  P. 
auricula  by  pollen  of  the  short-styled  P.  hirsuta 
yielded  capsules  containing  on  an  average  42  seeds  per 


*  '  Journ.  Linn.  Soc.  Bot.,'  vol.  viii.,  1864,  p.  93  to  end. 


CHAP.  II.  HYBRID  VERBASCUMS.  75 

capsule.  So  that  out  of  the  eight  possible  unions  be- 
tween the  two  forms  of  these  two  species,  six  were  utterly 
barren,  and  two  fairly  fertile.  We  have  seen  also 
the  same  sort  of  extraordinary  irregularity  in  the  re- 
sults of  my  twenty  different  crosses  (Tables  14  to  18), 
between  the  two  forms  of  the  oxlip,  primrose,  and  cow- 
slip. Mr.  Scott  remarks,  with  respect  to  the  results 
of  his  trials,  that  they  are  very  surprising,  as  they 
show  us  that  "  the  sexual  forms  of  a  species  manifest 
in  their  respective  powers  for  conjunction  with  those 
of  another  species,  physiological  peculiarities  which 
might  well  entitle  them,  by  the  criterion  of  fertility, 
to  specific  distinction." 

Finally,  although  P.  veris  and  vulgaris,  when  crossed 
legitimately,  and  especially  when  their  hybrid  offspring 
are  crossed  in  this  manner  with  both  parent-species, 
were  decidedly  more  fertile  than  when  crossed  in  an 
illegitimate  manner,  and  although  the  legitimate  cross 
effected  by  Mr.  Scott  between  P.  auricula  and  hirsuta 
was  more  fertile,  in  the  ratio  of  56  to  42,  than  the 
illegitimate  cross,  nevertheless  it  is  very  doubtful, 
from  the  extreme  irregularity  of  the  results  in  the 
various  other  hybrid  crosses  made  by  Mr.  Scott,  whether 
it  can  be  predicted  that  two  heterostyled  species  are 
generally  more  fertile  if  crossed  legitimately  (i.  e.  when 
opposite  forms  are  united)  than  when  crossed  illegiti- 
mately. 

Supplementary  Note  on  some  wild  hybrid  Verbascums. 

In  an  early  part  of  this  chapter  I  remarked  that  few 
other  instances  could  be  given  of  a  hybrid  spontane- 
ously arising  in  such  large  numbers,  and  over  so  wide  an 
extent  of  country,  as  that  of  the  common  oxlip ;  but  per- 
haps the  number  of  well-ascertained  cases  of  naturally 


76  HYBRID  VERBASCUMS.  CHAP.  II. 

produced  hybrid  willows  is  equally  great.*  Numerous 
spontaneous  hybrids  between  several  species  of  Cistus, 
found  near  Narbonne,  have  been  carefully  described 
by  M.  Timbal-Lagrave,f  and  many  hybrids  between  an 
Aceras  and  Orchis  have  been  observed  by  Dr.  Weddell.  \ 
In  the  genus  Verbascum,  hybrids  are  supposed  to  have 
often  originated  §  in  a  state  of  nature;  some  of  these  un- 
doubtedly are  hybrids,  and  several  hybrids  have  origi- 
nated in  gardens;  but  most  of  these  cases  require, ||  as 
Gartner  remarks,  verification.  Hence  the  following 
case  is  worth  recording,  more  especially  as  the  two 
species  in  question,  V.  thapsus  and  lyclinitis,  are  per- 
fectly fertile  when  insects  are  excluded,  showing  that 
the  stigma  of  each  flower  receives  its  own  pollen.  More- 
over the  flowers  offer  only  pollen  to  insects,  and  have 
not  been  rendered  attractive  to  them  by  secreting 
nectar. 

I  transplanted  a  young  wild  plant  into  my  garden 
for  experimental  purposes,  and  when  it  flowered  it 
plainly  differed  from  the  two  species  just  mentioned 
and  from  a  third  which  grows  in  this  neighbourhood.  I 
thought  that  it  was  a  strange  variety  of  V.  thapsus.  It 
attained  the  height  (by  measurement)  of  8  feet!  It 
was  covered  with  a  net,  and  ten  flowers  were  fertilised 
with  pollen  from  the  same  plant;  later  in  the  season, 
when  uncovered,  the  flowers  were  freely  visited  by 
pollen-collecting  bees;  nevertheless,  although  many 
capsules  were  produced,  not  one  contained  a  single 
seed.  During  the  following  year  this  same  plant  was 


*  Max  Wichura,    '  Die  Bastard-  ?  See,   for  instance,    the   '  Eng- 

befruchtung,    &c.,   der    Weiden,'  lish   Flora,'  by  Sir  J.   E.   Smith, 

1865-  1824,  vol.  i.  p.  307. 

t  '  Mem.  de  1' Acad.  des  Sciences  ||  See    Gartner,     '  Bastarderzeu- 

de  Toulouse,'  5«  serie,  torn.  v.  p.  28.  gung,'  1849,  p.  590. 

t '  Annales  des  Sc.  Nat.,'  3« serie, 
Bot.  torn,  xviii.  p.  6. 


CHAP.  II.  HYBRID  VERBASCUMS.  77 

left  uncovered  near  plants  of  V.  thapsus  and  lychnitis; 
but  again  it  did  not  produce  a  single  seed.  Four 
flowers,  however,  which  were  repeatedly  fertilised 
with  pollen  of  V.  lychnitis,  whilst  the  plant  was  tem- 
porarily kept  under  a  net,  produced  four  capsules, 
which  contained  five,  one,  two,  and  two  seeds;  at  the 
same  time  three  flowers  were  fertilised  with  pollen  of 
V.  thapsus,  and  these  produced  two,  two,  and  three 
seeds.  To  show  how  unproductive  these  seven  capsules 
were,  I  may  state  that  a  fine  capsule  from  a  plant  of 
V.  thapsus,  growing  close  by,  contained  above  700  seeds. 
These  facts  led  me  to  search  the  moderately  sized  field 
whence  my  plant  had  been  removed,  and  I  found  in  it 
many  plants  of  V.  thapsus  and  lychnitis,  as  well  as 
thirty-three  plants  intermediate  in  character  between 
these  two  species.  These  thirty-three  plants  differed 
much  from  one  another.  In  the  branching  of  the  stem 
they  more  closely  resembled  V.  lychnitis  than  V.  thap- 
sus, but  in  height  the  latter  species.  In  the  shape  of 
their  leaves  they  often  closely  approach  V.  lychnitis,  but 
some  had  leaves  extremely  woolly  on  the  upper  surface 
and  decurrent  like  those  of  V.  thapsus;  yet  the  degree 
of  woolliness  and  of  decurrency  did  not  always  go 
together.  In  the  petals  being  flat  and  remaining  open, 
and  in  the  manner  in  which  the  anthers  of  the  longer 
stamens  were  attached  to  the  filaments,  these  plants 
all  took  more  after  V.  lychnitis  than  V.  thapsus.  In 
the  yellow  colour  of  the  corolla  they  all  resembled  the 
latter  species.  On  the  whole,  these  plants  appeared 
to  take  rather  more  after  V.  lychnitis  than  V.  thapsus. 
On  the  supposition  that  they  were  hybrids,  it  is  not  an 
anomalous  circumstance  that  they  should  all  have  pro- 
duced yellow  flowers;  for  Gartner  crossed  white  and 
yellow-flowered  varieties  of  Verbascum,  and  the  off- 
spring thus  produced  never  bore  flowers  of  an  inter- 


Y8  HYBRID  VERBASCUMS.  CHAP.  II. 

mediate  tint,  but  either  pure  white  or  pure  yellow 
flowers,  generally  of  the  latter  colour.* 

My  observations  were  made  in  the  autumn;  so  that 
I  was  able  to  collect  some  half-matured  capsules  from 
twenty  of  the  thirty-three  intermediate  plants,  and 
likewise  capsules  of  the  pure  V.  lychnitis  and  tliapsus 
growing  in  the  same  field.  All  the  latter  were  filled 
with  perfect  but  immature  seeds,  whilst  the  capsules 
of  the  twenty  intermediate  plants  did  not  contain  one 
single  perfect  seed.  These  plants,  consequently,  were 
absolutely  barren.  From  this  fact, — from  the  one  plant 
which  was  transplanted  into  my  garden  yielding  when 
artificially  fertilised  with  pollen  from  V.  lychnitis  and 
thapsus  some  seeds,  though  extremely  few  in  number, — 
from  the  circumstances  of  the  two  pure  species  growing 
in  the  same  field, — and  from  the  intermediate  character 
of  the  sterile  plants,  there  can  be  no  doubt  that  they 
were  hybrids.  Judging  from  the  position  in  which 
they  were  chiefly  found,  I  am  inclined  to  believe  they 
were  descended  from  V.  thapsus  as  the  seed-bearer,  and 
V.  lychnitis  as  the  pollen-bearer. 

It  is  known  that  many  species  of  Verbascum,  when 
the  stem  is  jarred  or  struck  by  a  stick,  cast  off  their 
flowers,  f  This  occurs  with  V.  thapsus,  as  I  have  re- 
peatedly observed.  The  corolla  first  separates  from  its 
attachment,  and  then  the  sepals  spontaneously  bend 
inwards  so  as  to  clasp  the  ovarium,  pushing  off  the 
corolla  by  their  movement,  in  the  course  of  two  or 
three  minutes.  Nothing  of  this  kind  takes  place  with 
young  barely  expanded  flowers.  With  Verbascum  lych- 
nitis and,  as  I  believe,  V.  phceniceum  the  corolla  is  not 


* 'Bastarderzeugung,' p.  307.  Smith,'   vol.    ii.   p.    210.      I    was 

t  This    was   first    observed    hy  guided  to  these  references  hy  the 

Correa  de  Serra :    see  Sir    J.   E.  Rev.    W.    A.    Leighton,   who    ob- 

Smith's 'English  Flora,' 1824,  vol.  sorved    this    same    phenomenon 

i.  p.  311 ;  also  '  Life  of  Sir  J.  E.  with  V.  virgatum. 


CHAP.  II.  HYBRID  VERBASCUMS.  79 

cast  off,  however  often  and  severely  the  stem  may  be 
struck.  In  this  curious  property  the  above-described 
hybrids  took  after  V.  thapsus;  for  I  observed,  to  my 
surprise,  that  when  I  pulled  off  the  flower-buds  round 
the  flowers  which  I  wished  to  mark  with  a  thread,  the 
slight  jar  invariably  caused  the  corollas  to  fall  off. 

These  hybrids  are  interesting  under  several  points  of 
view.  First,  from  the  number  found  in  various  parts 
of  the  same  moderately-sized  field.  That  they  owed 
their  origin  to  insects  flying  from  flower  to  flower,  whilst 
collecting  pollen,  there  can  be  no  doubt.  Although  in- 
sects thus  rob  the  flowers  of  a  most  precious  substance, 
yet  they  do  great  good;  for  as  I  have  elsewhere 
shown,*  the  seedlings  of  V.  thapsus  raised  from  flowers 
fertilised  with  pollen  from  another  plant,  are  more 
vigorous  than  those  raised  from  self-fertilised  flowers. 
But  in  this  particular  instance  the  insects  did  great 
harm,  as  they  led  to  the  production  of  utterly  barren 
plants.  Secondly,  these  hybrids  are  remarkable  from 
differing  much  from  one  another  in  many  of  their 
characters;  for  hybrids  of  the  first  generation,  if 
raised  from  uncultivated  plants,  are  generally  uni- 
form in  character.  That  these  hybrids  belonged  to 
the  first  generation  we  may  safely  conclude,  from  the 
absolute  sterility  of  all  those  observed  by  me  in  a  state 
of  nature  and  of  the  one  plant  in  my  garden,  excepting 
when  artificially  and  repeatedly  fertilised  with  pure 
pollen,  and  then  the  number  of  seeds  produced  was 
extremely  small.  As  these  hybrids  varied  so  much,  an 
almost  perfectly  graduated  series  of  forms,  connecting 
together  the  two  widely  distinct  parent-species,  could 
easily  have  been  selected.  This  case,  like  that  of  the 
common  oxlip,  shows  that  botanists  ought  to  be  cau- 


*  '  The  Effects  of  Cross  and  Self- fertilisation,'  1876,  p.  89. 


80  HYBRID  VEEBASCUMS.  CHAP.  II. 

tious  in  referring  the  specific  identity  of  two  forms 
from  the  presence  of  intermediate  gradations;  nor 
would  it  be  easy  in  the  many  cases  in  which  hybrids  are 
moderately  fertile  to  detect  a  slight  degree  of  sterility  in 
such  plants  growing  in  a  state  of  nature  and  liable  to  be 
fertilised  by  either  parent-species.  Thirdly  and  lastly, 
these  hybrids  offer  an  excellent  illustration  of  a  state- 
ment made  by  that  admirable  observer  Gartner,  namely, 
that  although  plants  which  can  be  crossed  with  ease 
generally  produce  fairly  fertile  offspring,  yet  well- 
pronounced  exceptions  to  this  rule  occur;  and  here  we 
have  two  species  of  Verbascum  which  evidently  cross 
with  the  greatest  ease,  but  produce  hybrids  which  are 
excessively  sterile. 


CHAP.  III.  LINUM  GRANDIFLORUM.  81 


CHAPTER  III. 

HETEBOSTYLED  DIMORPHIC  PLANTS — continued. 

Linum  grandiflorum,  long-styled  form  utterly  sterile  with  own-form 
pollen — Linum  perenne,  torsion  of  the  pistils  in  the  long-styled 
form  alone — Homostyled  species  of  Linum — Pulmonaria  officinalis, 
singular  difference  in  self- fertility  hetween  the  English  and  German 
long-styled  plants — Pulmonaria  angustifolia  shown  to  be  a  distinct 
species,  long-styled  form  completely  self-sterile — Polygonum  fago- 
pyrum — Various  other  heterostyled  genera — Kubiacese — Mitchella 
repens,  fertility  of  the  flowers  in  pairs — Houstonia — Faramea, 
remarkable  difference  in  the  pollen-grains  of  the  two  forms ;  tor- 
sion of  the  stamens  in  the  short-styled  form  alone ;  development 
not  as  yet  perfect— The  heterostyled  structure  in  the  several 
Eubiaceous  genera  not  due  to  descent  in  common. 

IT  has  long  been  known  *  that  several  species  of 
Linum  present  two  forms,  and  having  observed  this 
fact  in  L.  flavum  more  than  thirty  years  ago,  I  was 
led,  after  ascertaining  the  nature  of  heterostylism  in 
Primula,  to  examine  the  first  species  of  Linum  which 
I  met  with,  namely,  the  beautiful  L.  grandiflorum. 
This  plant  exists  under  two  forms,  occurring  in  about 
equal  numbers,  which  differ  little  in  structure,  but 
greatly  in  function.  The  foliage,  corolla,  stamens,  and 
pollen-grains  (the  latter  examined  both  distended  with 
water  and  dry)  are  alike  in  the  two  forms  (Fig.  4). 
The  difference  is  confined  to  the  pistil;  in  the  short- 
styled  form  the  styles  and  the  stigmas  are  only  about 
half  the  length  of  those  in  the  long-styled.  A  more 


*Treviranus  has  shown  that  this    inal  paper,    'Bot.  Zeitung,'   1863, 
is  the  case  in  his  review  of  my  orig-    p.  189. 


82 


HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

important  distinction  is,  that  the  five  stigmas  in  the 
short-styled  form  diverge  greatly  from  one  another, 
and  pass  out  between  the  filaments  of  the  stamens, 
and  thus  lie  within  the  tube  of  the  corolla.  In  the 


Fig.  4. 


Long-styled  form.       Short-styled  form, 
s  s,  stigmas. 

LlNUM   GBANDIFLOEUM. 

long-styled  form  the  elongated  stigmas  stand  nearly  up- 
right, and  alternate  with  the  anthers.  In  this  latter 
form  the  length  of  the  stigmas  varies  considerably, 
their  upper  extremities  projecting  even  a  little  above 
the  anthers,  or  reaching  up  only  to  about  their  middle. 
Nevertheless,  there  is  never  the  slightest  difficulty  in 
distinguishing  between  the  two  forms;  for,  besides  the 
difference  in  the  divergence  of  the  stigmas,  those  of 
the  short-styled  form  never  reach  even  to  the  bases 
of  the  anthers.  In  this  form  the  papillae  on  the  stig- 
matic  surfaces  are  shorter,  darker-coloured,  and  more 
crowded  together  than  in  the  long-styled  form;  but 
these  differences  seem  due  merely  to  the  shortening 
of  the  stigma,  for  in  the  varieties  of  the  long-styled 
form  with  shorter  stigmas,  the  papillae  are  more  crowded 
and  darker-coloured  than  in  those  with  the  longer 


CHAP.  III.  j  LINUM  GRANDIFLORUM.  83 

stigmas.  Considering  the  slight  and  variable  differ- 
ences between  the  two  forms  of  this  Linum,  it  is  not 
surprising  that  hitherto  they  have  been  overlooked. 

In  1861  I  had  eleven  plants  in  my  garden,  eight  of 
which  were  long-styled,  and  three  short-styled.  Two 
very  fine  long-styled  plants  grew  in  a  bed  a  hundred 
yards  off  all  the  others,  and  separated  from  them  by  a 
screen  of  evergreens.  I  marked  twelve  flowers,  and 
placed  on  their  stigmas  a  little  pollen  from  the  short- 
styled  plants.  The  pollen  of  the  two  forms  is,  as 
stated,  identical  in  appearance;  the  stigmas  of  the 
long-styled  flowers  were  already  thickly  covered  with 
their  own  pollen — so  thickly  that  I  could  not  find  one 
bare  stigma,  and  it  was  late  in  the  season,  namely, 
September  15th.  Altogether,  it  seemed  almost  childish 
to  expect  any  result.  Nevertheless  from  my  experi- 
ments on  Primula,  I  had  faith,  and  did  not  hesitate  to 
make  the  trial,  but  certainly  did  not  anticipate  the 
full  result  which  was  obtained.  The  germens  of  these 
twelve  flowers  all  swelled,  and  ultimately  six  fine  cap- 
sules (the  seed  of  which  germinated  on  the  following 
year)  and  two  poor  capsules  were  produced;  only  four 
capsules  shanking  off.  These  same  two  long-styled 
plants  produced,  in  the  course  of  the  summer,  a 
vast  number  of  flowers,  the  stigmas  of  which  were 
covered  with  their  own  pollen;  but  they  all  proved 
absolutely  barren,  and  their  germens  did  not  even 
swell. 

The  nine  other  plants,  six  long-styled  and  three 
short-styled,  grew  not  very  far  apart  in  my  flower- 
garden.  Four  of  these  long-styled  plants  produced  no 
seed-capsules;  the  fifth  produced  two;  and  the  remain- 
ing one  grew  so  close  to  a  short-styled  plant  that 
their  branches  touched,  and  this  produced  twelve  cap- 
sules, but  they  were  poor  ones.  The  case  was  different 


84       HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

with  the  short-styled  plants.  The  one  which  grew 
close  to  the  long-styled  plant  produced  ninety-four 
imperfectly  fertilised  capsules  containing  a  multitude 
of  bad  seeds,  with  a  moderate  number  of  good  ones. 
The  two  other  short-styled  plants  growing  together 
were  small,  being  partly  smothered  by  other  plants; 
they  did  not  stand  very  close  to  any  long-styled  plants, 
yet  they  yielded  together  nineteen  capsules.  These 
facts  seem  to  show  that  the  short-styled  plants  are  more 
fertile  with  their  own  pollen  than  are  the  long-styled, 
and  we  shall  immediately  see  that  this  probably  is  the 
case.  But  I  suspect  that  the  difference  in  fertility  be- 
tween the  two  forms  was  in  this  instance  in  part  due  to 
a  distinct  cause.  I  repeatedly  watched  the  flowers,  and 
only  once  saw  a  humble-bee  momentarily  alight  on 
one,  and  then  fly  away.  If  bees  had  visited  the  several 
plants,  there  cannot  be  a  doubt  that  the  four  long- 
styled  plants,  which  did  not  produce  a  single  capsule, 
would  have  borne  an  abundance.  But  several  times 
I  saw  small  diptera  sucking  the  flowers;  and  these 
insects,  though  not  visiting  the  flowers  with  anything 
like  the  regularity  of  bees,  would  carry  a  little  pollen 
from  one  form  to  the  other,  especially  when  growing 
near  together;  and  the  stigmas  of  the  short-styled 
plants,  diverging  within  the  tube  of  the  corolla,  would 
be  more  likely  than  the  upright  stigmas  of  the  long- 
styled  plants,  to  receive  a  small  quantity  of  pollen  if 
brought  to  them  by  small  insects.  Moreover  from  the 
greater  number  of  the  long-styled  than  of  the  short- 
styled  plants  in  the  garden,  the  latter  would  be  more 
likely  to  receive  pollen  from  the  long-styled,  than  the 
long-styled  from  the  short-styled. 

In  1862  I  raised  thirty-four  plants  of  this  Linum  in 
a  hot-bed;  and  these  consisted  of  seventeen  long-styled 
and  seventeen  short-styled  forms.  Seed  sown  later  in  the 


CHAP.  III.  LINUM  GRANDIFLORUM.  85 

flower-garden  yielded  seventeen  long-styled  and  twelve 
short-styled  forms.  These  facts  justify  the  statement 
that  the  two  forms  are  produced  in  about  equal  num- 
bers. The  thirty-four  plants  of  the  first  lot  were  kept 
under  a  net  which  excluded  all  insects,  except  such 
minute  ones  as  Thrips.  I  fertilised  fourteen  long-styled 
flowers  legitimately,  with  pollen  from  the  short-styled, 
and  got  eleven  fine  seed-capsules,  which  contained  on 
an  average  8.6  seeds  per  capsule,  but  only  5.6  appeared 
to  be  good.  It  may  be  well  to  state  that  ten  seeds  are 
the  maximum  production  for  a  capsule,  and  that  our 
climate  cannot  be  very  favourable  to  this  North- African 
plant.  On  three  occasions  the  stigmas  of  nearly  a 
hundred  flowers  were  fertilised  illegitimately  with  their 
own-form  pollen,  taken  from  separate  plants,  so  as  to 
prevent  any  possible  ill  effects  from  close  inter-breed- 
ing. Many  other  flowers  were  also  produced,  which,  as 
before  stated,  must  have  received  plenty  of  their  own 
pollen;  yet  from  all  these  flowers,  borne  by  the  seven- 
teen long-styled  plants,  only  three  capsules  were  pro- 
duced. One  of  these  included  no  seed,  and  the  other 
two  together  gave  only  five  good  seeds.  It  is  probable 
that  this  miserable  product  of  two  half -fertile  capsules 
from  the  seventeen  plants,  each  of  which  must  have 
produced  at  least  fifty  or  sixty  flowers,  resulted  from 
their  fertilisation  with  pollen  from  the  short-styled 
plants  by  the  aid  of  Thrips;  for  I  made  a  great  mis- 
take in  keeping  the  two  forms  under  the  same  net, 
with  their  branches  often  interlocking;  and  it  is  sur- 
prising that  a  greater  number  of  flowers  were  not  acci- 
dentally fertilised. 

Twelve  short-styled  flowers  were  in  this  instance 
castrated,  and  afterwards  fertilised  legitimately  with 
pollen  from  the  long-styled  form;  and  they  produced 
seven  fine  capsules.  These  included  on  an  average  7.6 


8G       HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 

seeds,  but  of  apparently  good  seed  only  4.3  per  cap- 
sule. At  three  separate  times  nearly  a  hundred  flowers 
were  fertilised  illegitimately  with  their  own-form  pollen, 
taken  from  separate  plants;  and  numerous  other 
flowers  were  produced,  many  of  which  must  have  re- 
ceived their  own  pollen.  From  all  these  flowers  on 
the  seventeen  short-styled  plants  only  fifteen  capsules 
were  produced,  of  which  only  eleven  contained  any 
good  seed,  on  an  average  4.2  per  capsule.  As  remarked 
in  the  case  of  the  long-styled  plants,  some  even  of  these 
capsules  were  perhaps  the  product  of  a  little  pollen 
accidentally  fallen  from  the  adjoining  flowers  of  the 
other  form  on  to  the  stigmas,  or  transported  by  Thrips. 
Nevertheless  the  short-styled  plants  seem  to  be  slightly 
more  fertile  with  their  own  pollen  than  the  long-styled, 
in  the  proportion  of  fifteen  capsules  to  three;  nor  can 
this  difference  be  accounted  for  by  the  short-styled 
stigmas  being  more  liable  to  receive  their  own  pollen 
than  the  long-styled,  for  the  reverse  is  the  case.  The 
greater  self-fertility  of  the  short-styled  flowers  was  like- 
wise shown  in  1861  by  the  plants  in  my  flower-garden, 
which  were  left  to  themselves,  and  were  but  sparingly 
visited  by  insects. 

On  account  of  the  probability  of  some  of  the  flowers 
on  the  plants  of  both  forms,  which  were  covered  under 
the  same  net,  having  been  legitimately  fertilised  in 
an  accidental  manner,  the  relative  fertility  of  the 
two  legitimate  and  two  illegitimate  unions  cannot 
be  compared  with  certainty;  but  judging  from  the 
number  of  good  seeds  per  capsule,  the  difference  was 
at  least  in  the  ratio  of  100  to  7,  and  probably  much 
greater. 

Hildebrand  tested  my  results,  but  only  on  a  single 
short-styled  plant,  by  fertilising  many  flowers  with 
their  own- form  pollen;  and  these  did  not  produce  any 


CHAP.  III.  LINUM  GEANDIFLORUM.  87 

seed.  This  confirms  my  suspicion  that  some  of  the 
few  capsules  produced  by  the  foregoing  seventeen  short- 
styled  plants  were  the  product  of  accidental  legitimate 
fertilisation.  Other  flowers  on  the  same  plant  were 
fertilised  by  Hildebrand  with  pollen  from  the  long- 
styled  form,  and  all  produced  fruit.* 

The  absolute  sterility  (judging  from  the  experi- 
ments of  1861)  of  the  long-styled  plants  with  their 
own-form  pollen  led  me  to  examine  into  its  apparent 
cause;  and  the  results  are  so  curious  that  they  are 
worth  giving  in  detail.  The  experiments  were  tried 
on  plants  grown  in  pots  and  brought  successively  into 
the  house. 

First.  Pollen  from  a  short-styled  plant  was  placed 
on  the  five  stigmas  of  a  long-styled  flower,  and  these, 
after  thirty  hours,  were  found  deeply  penetrated  by 
a  multitude  of  pollen-tubes,  far  too  numerous  to  be 
counted;  the  stigmas  had  also  become  discoloured 
and  twisted.  I  repeated  this  experiment  on  another 
flower,  and  in  eighteen  hours  the  stigmas  were  pene- 
trated by  a  multitude  of  long  pollen-tubes.  This  is 
what  might  have  been  expected,  as  the  union  is  a 
legitimate  one.  The  converse  experiment  was  likewise 
tried,  and  pollen  from  a  long-styled  flower  was  placed 
on  the  stigmas  of  a  short-styled  flower,  and  in  twenty- 
four  hours  the  stigmas  were  discoloured,  twisted,  and 
penetrated  by  numerous  pollen-tubes;  and  this,  again, 
is  what  might  have  been  expected,  as  the  union  was 
a  legitimate  one. 

Secondly.  Pollen  from  a  long-styled  flower  was 
placed  on  all  five  stigmas  of  a  long-styled  flower  on  a 
separate  plant :  after  nineteen  hours  the  stigmas  were  dis- 
sected, and  only  a  single  pollen-grain  had  emitted  a  tube, 


*  '  Bot.  Zeitung,'  Jan.  1,  1864,  p.  2. 


88       HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

and  this  was  a  very  short  one.  To  make  sure  that  the 
pollen  was  good,  I  took  in  this  case,  and  in  most  of 
the  other  cases,  pollen  either  from  the  same  anther  or 
from  the  same  flower,  and  proved  it  to  be  good  by 
placing  it  on  the  stigma  of  a  short-styled  plant,  and 
found  numerous  pollen-tubes  emitted. 

Thirdly.  Eepeated  last  experiment,  and  placed  own- 
form  pollen  on  all  five  stigmas  of  a  long-styled  flower; 
after  nineteen  hours  and  a  half,  not  one  single  grain 
had  emitted  its  tube. 

Fourthly.  Eepeated  the  experiment,  with  the  same 
result  after  twenty-four  hours. 

Fifthly.  Eepeated  last  experiment,  and,  after  leaving 
pollen  on  for  nineteen  hours,  put  on  an  additional 
quantity  of  own-form  pollen  on  all  five  stigmas.  After 
an  interval  of  three  days,  the  stigmas  were  examined, 
and,  instead  of  being  discoloured  and  twisted,  they 
were  straight  and  fresh-coloured.  Only  one  grain  had 
emitted  a  quite  short  tube,  which  was  drawn  out  of 
the  stigmatic  tissue  without  being  ruptured. 

The  following  experiments  are  more  striking: — 

Sixthly.  I  placed  own-form  pollen  on  three  of  the 
stigmas  of  the  long-styled  flower,  and  pollen  from  a 
short-styled  flower  on  the  other  two  stigmas.  After 
twenty-two  hours  these  two  stigmas  were  discoloured, 
slightly  twisted,  and  penetrated  by  the  tubes  of  nu- 
merous pollen-grains:  the  other  three  stigmas,  covered 
with  their  own-form  pollen,  were  fresh,  and  all  the 
pollen-grains  were  loose ;  but  I  did  not  dissect  the  whole 
stigma. 

Seventhly.  Experiment  repeated  in  the  same  man- 
ner, with  the  same  result. 

Eighthly.  Experiment  repeated,  but  the  stigmas  were 
carefully  examined  after  an  interval  of  only  five  hours 
and  a  half.  The  two  stigmas  with  pollen  from  a  short- 


CHAP.  III.  LINUM  GRANDIFLORUM.  89 

styled  flower  were  penetrated  by  innumerable  tubes, 
which  were  as  yet  short,  and  the  stigmas  themselves  were 
not  at  all  discoloured.  The  three  stigmas  covered  with 
their  own-form  pollen  were  not  penetrated  by  a  single 
pollen-tube. 

Ninthly.  Put  pollen  of  a  short-styled  flower  on  a 
single  long-styled  stigma,  and  own-form  pollen  on  the 
other  four  stigmas;  after  twenty-four  hours  the  one 
stigma  was  somewhat  discoloured  and  twisted,  and  pene- 
trated by  many  long  tubes:  the  other  four  stigmas 
were  quite  straight  and  fresh;  but  on  dissecting  them 
I  found  that  three  pollen-grains  had  protruded  very 
short  tubes  into  the  tissue. 

TentUly.  Eepeated  the  experiment,  with  the  same 
result  after  twenty-four  hours,  excepting  that  only  two 
own-form  grains  had  penetrated  the  stigmatic  tissue 
with  their  tubes  to  a  very  short  depth.  The  cne  stigma, 
which  was  deeply  penetrated  by  a  multitude  of  tubes 
from  the  short-styled  pollen,  presented  a  conspicuous 
difference  in  being  much  curled,  half-shrivelled,  and 
discoloured,  in  comparison  with  the  other  four  straight 
and  bright  pink  stigmas. 

I  could  add  other  experiments:  but  those  now 
given  amply  suffice  to  show  that  the  pollen-grains  of 
a  short-styled  flower  placed  on  the  stigma  of  a  long- 
styled  flower  emit  a  multitude  of  tubes  after  an  in- 
terval of  from  five  to  six  hours,  and  penetrate  the 
tissue  ultimately  to  a  great  depth;  and  that  after 
twenty-four  hours  the  stigmas  thus  penetrated  change 
colour,  become  twisted,  and  appear  half-withered.  On 
the  other  hand,  pollen-grains  from  a  long-styled  flower 
placed  on  its  own  stigmas,  do  not  emit  their  tubes 
after  an  interval  of  a  day,  or  even  three  days;  or  at 
most  only  three  or  four  grains  out  of  a  multitude  emit 
their  tubes,  and  these  apparently  never  penetrate  the 


90       HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

stigmatic  tissue  deeply,  and  the  stigmas  themselves  do 
not  soon  become  discoloured  and  twisted. 

This  seems  to  me  a  remarkable  physiological  fact. 
The  pollen-grains  of  the  two  forms  are  undistinguish- 
able' under  the  microscope;  the  stigmas  differ  only  in 
length,  degree  of  divergence,  and  in  the  size,  shade  of 
colour,  and  approximation  of  their  papillae,  these  latter 
differences  being  variable  and  apparently  due  merely 
to  the  degree  of  elongation  of  the  stigma.  Yet  we 
plainly  see  that  the  two  kinds  of  pollen  and  the  two 
stigmas  are  widely  dissimilar  in  their  mutual  reaction 
— the  stigmas  of  each  form  being  almost  powerless  on 
their  own  pollen,  but  causing,  through  some  myste- 
rious influence,  apparently  by  simple  contact  (for  I 
could  detect  no  viscid  secretion),  the  pollen-grains  of 
the  opposite  form  to  protrude  their  tubes.  It  may  be 
said  that  the  two  pollens  and  the  tAvo  stigmas  mutually 
recognise  each  other  by  some  means.  Taking  fertility 
as  the  criterion  of  distinctness,  it  is  no  exaggeration  to 
say  that  the  pollen  of  the  long-styled  Linum  grandi- 
florum  (and  conversely  that  of  the  other  form)  has  been 
brought  to  a  degree  of  differentiation,  with  respect  to 
its  action  on  the  stigma  of  the  same  form,  correspond- 
ing with  that  existing  between  the  pollen  and  stigma 
of  species  belonging  to  distinct  genera. 

Linum  perenne. — This  species  is  conspicuously  hete- 
rostyled,  as  has  been  noticed  by  several  authors.  The 
pistil  in  the  long-styled  form  is  nearly  twice  as  long  as 
that  of  the  short-styled.  In  the  latter  the  stigmas  are 
smaller  and,  diverging  to  a  greater  degree,  pass  out 
low  down  between  the  filaments.  I  could  detect  no 
difference  in  the  two  forms  in  the  size  of  the  stigmatic 
papilla?.  In  the  long-styled  form  alone  the  stigmatic 
surfaces  of  the  mature  pistils  twist  round,  so  as  to  face 
the  circumference  of  the  flower;  but  to  this  point  I 


CHAP.  III.  LINUM  PERENNE.  91 

shall  presently  return.  Differently  from  what  occurs  in 
L.  grandiflorum,  the  long-styled  flowers  have  stamens 
hardly  more  than  half  the  length  of  those  in  the  short- 
styled.  The  size  of  the  pollen-grains  is  rather  variable ; 
after  some  doubt,  I  have  come  to  the  conclusion  that 
there  is  no  uniform  difference  between  the  grains  in 
the  two  forms.  The  long  stamens  in  the  short-styled 
form  project  to  some  height  above  the  corolla,  and 
their  filaments  are  coloured  blue  apparently  from  ex- 
posure to  the  light.  The  anthers  of  the  longer  stamens 
correspond  in  height  with  the  lower  part  of  the  stigmas 
of  the  long-styled  flowers;  and  the  anthers  of  the 
shorter  stamens  of  the  latter  correspond  in  the  same 
manner  in  height  with  the  stigmas  of  the  short-styled 
flowers. 

I  raised  from  seed  twenty-six  plants,  of  which  twelve 
proved  to  be  long-styled  and  fourteen  short-styled. 
They  flowered  well,  but  were  not  large  plants.  As  I 
did  not  expect  them  to  flower  so  soon,  I  did  not  trans- 
plant them,  and  they  unfortunately  grew  with  their 
branches  closely  interlocked.  All  the  plants  were 
covered  under  the  same  net,  excepting  one  of  each 
form.  Of  the  flowers  on  the  long-styled  plants,  twelve 
were  illegitimately  fertilised  with  their  own-form  pol- 
len, taken  in  every  case  from  a  separate  plant;  and  not 
one  set  a  seed-capsule:  twelve  other  flowers  were  legi- 
timately fertilised  with  pollen  from  short-styled  flowers ; 
and  they  set  nine  capsules,  each  including  on  an 
average  7  good  seeds,  ten  being  the  maximum  number 
ever  produced.  Of  the  flowers  on  the  short-styled 
plants,  twelve  were  illegitimately  fertilised  with  own- 
form  pollen,  and  they  yielded  one  capsule,  including 
only  3  good  seeds;  twelve  other  flowers  were  legiti- 
mately fertilised  with  pollen  from  long-styled  flowers, 
and  these  produced  nine  capsules,  but  one  was  bad; 


92       HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

the  eight  good  capsules  contained  on  an  average  8  good 
seeds  each.  Judging  from  the  number  of  seeds  per 
capsule,  the  fertility  of  the  two  legitimate  to  that  of 
the  two  illegitimate  unions  is  as  100  to  20. 

The  numerous  flowers  on  the  eleven  long-styled 
plants  under  the  net,  which  were  not  fertilised,  produced 
only  three  capsules,  including  8,  4,  and  1  good  seeds. 
Whether  these  three  capsules  were  the  product  of  acci- 
dental legitimate  fertilisation,  owing  to  the  branches 
of  the  plants  of  the  two  forms  interlocking,  I  will  not 
pretend  to  decide.  The  single  long-styled  plant  which 
was  left  uncovered,  and  grew  close  by  the  uncovered 
short-styled  plant,  produced  five  good  pods;  but  it  was 
a  poor  and  small  plant. 

The  flowers  borne  on  the  thirteen  short-styled  plants 
under  the  net,  which  were  not  fertilised,  produced 
twelve  capsules,  containing  on  an  average  5.6  seeds. 
As  some  of  these  capsules  were  very  fine,  and  as  five 
were  borne  on  one  twig,  I  suspect  that  some  minute 
insect  had  accidentally  got  under  the  net  and  had 
brought  pollen  from  the  other  form  to  the  flowers  which 
produced  this  little  group  of  capsules.  The  one  un- 
covered short-styled  plant  which  grew  close  to  the  un-* 
covered  long-styled  plant  yielded  twelve  capsules. 

From  these  facts  we  have  some  reason  to  believe,  as 
in  the  case  of  L.  grandiflorum,  that  the  short-styled 
plants  are  in  a  slight  degree  more  fertile  with  their 
own  pollen  than  are  the  long-styled  plants.  Anyhow 
we  have  the  clearest  evidence  that  the  stigmas  of  each 
form  require  for  full  fertility  that  pollen  from  the  sta- 
mens of  corresponding  height  belonging  to  the  opposite 
form  should  be  brought  to  them. 

Hildebrand,  in  the  paper  lately  referred  to,  confirms 
my  results.  He  placed  a  short-styled  plant  in  his 
house,  and  fertilised  about  20  flowers  with  their  own 


CHAP.  III.  LINUM  PERENNE.  93 

pollen,  and  about  30  with  pollen  from  another  plant 
belonging  to  the  same  form,  and  these  50  flowers  did 
not  set  a  single  capsule.  On  the  other  hand  he  ferti- 
lised about  30  flowers  with  pollen  from  the  long-styled 
form,  and  these,  with  the  exception  of  two,  yielded 
capsules,  containing  good  seeds. 

It  is  a  singular  fact,  in  contrast  with  what  occurred 
in  the  case  of  L.  grandiflorum,  that  the  pollen-grains  of 
both  forms  of  L.  perenne,  when  placed  on  their  own- 
form  stigmas,  emitted  their  tubes,  though  this  action 
did  not  lead  to  the  production  of  seeds.  After  an  in- 
terval of  eighteen  hours,  the  tubes  penetrated  the  stig- 
matic  tissue,  but  to  what  depth  I  did  not  ascertain. 
In  this  case  the  impotence  of  the  pollen-grains  on  their 
own  stigmas  must  have  been  due  either  to  the  tubes 
not  reaching  the  ovules,  or  to  their  not  acting  properly 
after  reaching  them. 

The  plants  both  of  L.  perenne  and  grandiflorum 
grew,  as  already  stated,  with  their  branches  interlocked, 
and  with  scores  of  flowers  of  the  two  forms  close  to- 
gether ;  they  were  covered  by  a  rather  coarse  net,  through 
which  the  wind,  when  high,  passed ;  and  such  minute  in- 
sects as  Thrips  could  not,  of  course,  be  excluded ;  yet  we 
have  seen  that  the  utmost  possible  amount  of  accidental 
fertilisation  on  seventeen  long-styled  plants  in  the  one 
case,  and  on  eleven  long-styled  plants  in  the  other, 
resulted  in  the  production,  in  each  case,  of  three 
poor  capsules;  so  that  when  the  proper  insects  are  ex- 
cluded, the  wind  does  hardly  anything  in  the  way  of 
carrying  pollen  from  plant  to  plant.  I  allude  to  this 
fact  because  botanists,  in  speaking  of  the  fertilisation 
of  various  flowers,  often  refer  to  the  wind  or  to  insects 
as  if  the  alternative  were  indifferent.  This  view,  ac- 
cording to  my  experience,  is  entirely  erroneous.  "When 
the  wind  is  the  agent  in  carrying  pollen,  either  from 


9  i       HETEEOSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

one  sex  to  the  other,  or  from  hermaphrodite  to  herma- 
phrodite, we  can  recognise  structure  as  manifestly 
adapted  to  its  action  as  to  that  of  insects  when  these 
are  the  carriers.  We  see  adaptation  to  the  wind  in  the 
incoherence  of  the  pollen, — in  the  inordinate  quantity 
produced  (as  in  the  Conifera,  Spinage,  &c.), — in  the 
dangling  anthers  well  fitted  to  shake  out  the  pollen, — 
in  the  absence  or  small  size  of  the  perianth, — in  the 
protrusion  of  the  stigmas  at  the  period  of  fertilisation, 
— in  the  flowers  being  produced  before  they  are  hidden 
by  the  leaves, — and  in  the  stigmas  being  downy  or 
plumose  (as  in  the  Gramineae,  Docks,  &c.),  so  as  to 
secure  the  chance-blown  grains.  In  plants  which  are 
fertilised  by  the  wind,  the  flowers  do  not  secrete  nectar, 
their  pollen  is  too  incoherent  to  be  easily  collected  by 
insects,  they  have  not  bright-coloured  corollas  to  serve 
as  guides,  and  they  are  not,  as  far  as  I  have  seen,  visited 
by  insects.  When  insects  are  the  agents  of  fertilisa- 
tion (and  this  is  incomparably  the  more  frequent  case 
with  hermaphrodite  plants),  the  wind  plays  no  part, 
but  we  see  an  endless  number  of  adaptations  to  ensure 
the  safe  transport  of  the  pollen  by  the  living  workers. 
These  adaptations  are  most  easily  recognised  in  irregu- 
lar flowers;  but  they  are  present  in  regular  flowers, 
of  which  those  of  Linum  offer  a  good  instance,  as  I  will 
now  endeavour  to  show. 

I  have  already  alluded  to  the  rotation  of  each  sepa- 
rate stigma  in  the  long-styled  form  of  Linum  perenne. 
In  both  forms  of  the  other  heterostyled  species  and  in 
the  homostyled  species  of  Linum  which  I  have  seen, 
the  stigmatic  surfaces  face  the  centre  of  the  flower, 
with  the  furrowed  backs  of  the  stigmas,  to  which  the 
styles  are  attached,  facing  outwards.  This  is  the  case 
with  the  stigmas  of  the  long-styled  flowers  of  L. 
perenne  whilst  in  bud.  But  by  the  time  the  flowers 


CHAP.  III.  LINUM  PERENNE.  95 

have  expanded,  the  five  stigmas  twist  round  so  as  to 
face  the  circumference,  owing  to  the  torsion  of  that 
part  of  the  style  which  lies  beneath  the  stigma.  I 
should  state  that  the  five  stigmas  do  not  always  turn 
round  completely,  two  or  three  sometimes  facing 
only  obliquely  outwards.  My  observations  were  made 
during  October;  and  it  is  not  improbable  that  earlier 
in  the  season  the  torsion  would  have  been  more  com- 
plete; for  after  two  or  three  cold  and  wet  days  the 
movement  was  very  imperfectly  performed.  The 
flowers  should  be  examined  shortly  after  their  ex- 
pansion, as  their  duration  is  brief;  as  soon  as  they 
begin  to  wither,  the  styles  become  spirally  twisted  all 
together,  the  original  position  of  the  parts  being  thus 
lost. 

He  who  will  compare  the  structure  of  the  whole 
flower  in  both  forms  of  L.  perenne  and  grandiflorum, 
and,  as  I  may  add  of  L.  flavum,  will  not  doubt  about 
the  meaning  of  this  torsion  of  the  styles  in  the  one 
form  alone  of  L.  perenne,  as  well  as  the  meaning  of 
the  divergence  of  the  stigmas  in  the  short-styled 
form  of  all  three  species.  It  is  absolutely  necessary, 
as  we  know,  that  insects  should  carry  pollen  from 
the  flowers  of  the  one  form  reciprocally  to  those  of 
the  other.  Insects  are  attracted  by  five  drops  of 
nectar,  secreted  exteriorly  at  the  base  of  the  stamens, 
so  that  to  reach  these  drops  they  must  insert  their 
proboscides  outside  the  ring  of  broad  filaments,  be- 
tween them  and  the  petals.  In  the  short-styled  form 
of  the  above  three  species,  the  stigmas  face  the  axis  of 
the  flower;  and  had  the  styles  retained  their  original 
upright  and  central  position,  not  only  would  the  stig- 
mas have  presented  their  backs  to  the  insects  which 
sucked  the  flowers,  but  their  front  and  fertile  surfaces 
would  have  been  separated  from  the  entering  insects 


96       HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

by  the  ring  of  broad  filaments,  and  would  never  have 
received  any  pollen.  As  it  is,  the  styles  diverge  and 
pass  out  between  the  filaments.  After  this  movement 
the  short  stigmas  lie  within  the  tube  of  the  corolla; 
and  their  papillous  surfaces  being  now  turned  upwards 
are  necessarily  brushed  by  every  entering  insect,  and 
thus  receive  the  required  pollen. 

In  the  long-styled  form  of  L.  grandiflorum,  the 
almost  parallel  or  slightly  diverging  anthers  and 
stigmas  project  a  little  above  the  tube  of  the  somewhat 
concave  flower;  and  they  stand  directly  over  the  open 
space  leading  to  the  drops  of  nectar.  Consequently 
when  insects  visit  the  flowers  of  either  form  (for  the 
stamens  in  this  species  occupy  the  same  position  in 
both  forms),  they  will  get  their  foreheads  or  proboscides 
well  dusted  with  the  coherent  pollen.  As  soon  as  they 
visit  the  flowers  of  the  long-styled  form  they  will  neces- 
sarily leave  pollen  on  the  proper  surface  of  the  elon- 
gated stigmas;  and  when  they  visit  the  short-styled 
flowers,  they  will  leave  pollen  on  the  upturned  stig- 
matic  surfaces.  Thus  the  stigmas  of  both  forms  will 
receive  indifferently  the  pollen  of  both  forms;  but  we 
know  that  the  pollen  alone  of  the  opposite  form  causes 
fertilisation. 

In  the  case  of  L.  perenne,  affairs  are  arranged  more 
perfectly;  for  the  stamens  in  the  two  forms  stand  at 
different  heights,  so  that  pollen  from  the  anthers  of 
the  longer  stamens  will  adhere  to  one  part  of  an  in- 
sect's body,  and  will  afterwards  be  brushed  off  by  the 
rough  stigmas  of  the  longer  pistils;  whilst  pollen  from 
the  anthers  of  the  shorter  stamens  will  adhere  to  a 
different  part  of  the  insect's  body,  and  will  afterwards 
be  brushed  off  by  the  stigmas  of  the  shorter  pistils ;  and 
this  is  what  is  required  for  the  legitimate  fertilisa- 
tion of  both  forms.  The  corolla  of  L.  perenne  is  more 


CHAP.  III. 


LINUM  PERENNE. 


9T 


expanded  than  that  of  L.  grandiflorum,  and  the  stigmas 
of  the  long-styled  form  do  not  diverge  greatly  from 
one  another;  nor  do  the  stamens  of  either  form. 
Hence  insects,  especially  rather  small  ones,  will  not 
insert  their  proboscides  between  the  stigmas  of  the 
long-styled  form,  nor  between  the  anthers  of  either 
form  (Fig.  5),  but  will  strike  against  them,  at  nearly 

Fig.  5. 


Long-styled  form  of  L.  PEEEXXE,  var.  Austriacum,  in  its  early  condi- 
tion before  the  stigmas  have  rotated.  The  petals  and  calyx  have 
been  removed  on  the  near  side.* 


right  angles,  with  the  backs  of  their  head  or  thorax. 
Now,  in  the  long-styled  flowers,  if  each  stigma  did 
not  rotate  on  its  axis,  insects  in  visiting  them  would 
strike  their  heads  against  the  backs  of  the  stigmas;  as 
it  is,  they  strike  against  that  surface  which  is  covered 
with  papillas,  with  their  heads  already  charged  with 


*  I  neglected    to  get  drawings  from  published  engravings.     His 

made  from  fresh  flowers  of  the  two  well-known  skill  ensures  accuracy 

forms.     But  Mr.  Fitch  has  made  in  the  proportional  size    of  the 

the  above  sketch  of  a  long-styled  parts, 
flower  from  dried  specimens  and 


98       HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 

pollen  from  the  stamens  of  corresponding  height  borne 
by  the  flowers  of  the  other  form,  and  legitimate  fertilisa- 
tion is  thus  ensured. 

Thus  we  can  understand  the  meaning  of  the  torsion 
of  the  styles  in  the  long-styled  flowers  alone^  as  well 
as  their  divergence  in  the  short-styled  flowers. 

One  other  point  is  worth  notice.  In  botanical  works 
many  flowers  are  said  to  be  fertilised  in  the  bud.  This 
statement  generally  rests,  as  far  as  I  can  discover,  on 
the  anthers  opening  in  the  bud;  no  evidence  being 
adduced  that  the  stigma  is  at  this  period 'mature,  or 
that  it  is  not  subsequently  acted  on  by  pollen  brought 
from  other  flowers.  In  the  case  of  Cephalanthera 
grandiflora  I  have  shown*  that  precocious  and  partial 
self-fertilisation,  with  subsequent  full  fertilisation,  is 
the  regular  course  of  events.  The  belief  that  the 
flowers  of  many  plants  are  fertilised  in  the  bud,  that 
is,  are  perpetually  self-fertilised,  is  a  most  effectual  bar 
to  understanding  their  real  structure.  I  am,  however, 
far  from  wishing  to  assert  that  some  flowers,  during 
certain  seasons,  are  not  fertilised  in  the  bud;  for  I 
have  reason  to  believe  that  this  is  the  case.  A  good 
observer,!  resting  his  belief  on  the  usual  kind  of  evi- 
dence, states  that  in  Linum  Austriacum  (which  is 
heterostyled,  and  is  considered  by  Planchon  as  a  variety 
of  L.  perenne}  the  anthers  open  the  evening  before 
the  expansion  of  the  flowers,  and  that  the  stigmas  are 
then  almost  always  fertilised.  Now  we  know  positively 
that,  so  far  from  Linum  perenne  being  fertilised  by  its 
own  pollen  in  the  bud,  its  own  pollen  is  as  powerless 
on  the  stigma  as  so  much  inorganic  dust. 

Linum  flavum. — The  pistil  of  the  long-styled  form 
of  this  species  is  nearly  twice  as  long  as  that  of 


*  'Fertilisation  of  Orchids,'   p.'        t' Etudes  <=nr  la  G6ogr.   Bot.,' 
108,  2nd  edit.  1877,  p.  84.  H.  Lecoq,  1856,  torn.  v.  p.  325. 


CHAP.  III.  LIXUM  FLAVUM.  90 

the  short-styled;  the  stigmas  are  longer  and  the 
papillae  coarser.  In  the  short-styled  form  the  stigmas 
diverge  and. pass  out  between  the  filaments,  as  in  the 
previous  species.  The  stamens  in  the  two  forms  differ 
in  length;  and,  what  is  singular,  the  anthers  of  the 
longer  stamens  are  not  so  long  as  those  of  the  other 
form;  so  that  in  the  short-styled  form  both  the  stigmas 
and  the  anthers  are  shorter  than  in  the  long-styled 
form.  The  pollen-grains  of  the  two  forms  do  not  differ 
in  size.  As  this  species  is  propagated  by  cuttings, 
generally  all  the  plants  in  the  same  garden  belong  to 
the  same  form.  I  have  inquired,  but  have  never  heard 
of  its  seeding  in  this  country.  Certainly  my  own  plants 
never  produced  a  single  seed  as  long  as  I  possessed 
only  one  of  the  two  forms.  After  considerable  search  I 
procured  both  forms,  but  from  want  of  time  only  a  few 
experiments  were  made.  Two  plants  of  the  two  forms 
were  planted  some  way  apart  in  my  garden,  and  were 
not  covered  by  nets.  Three  flowers  on  the  long-styled 
plant  were  legitimately  fertilised  with  pollen  from  the 
short-styled  plant,  and  one  of  them  set  a  fine  capsule. 
Xo  other  capsules  were  produced  by  this  plant.  Three 
flowers  on  the  short-styled  plant  were  legitimately 
fertilised  with  pollen  from  the  long-styled,  and  all 
three  produced  capsules,  containing  respectively  no 
less  than  8,  9,  and  10  seeds.  Three  other  flowers  on 
this  plant,  which  had  not  been  artificially  fertilised, 
produced  capsules  containing  5,  1,  and  5  seeds;  and 
it  is  quite  possible  that  pollen  may  have  been 
brought  to  them  by  insects  from  the  long-styled  plant 
growing  in  the  same  garden.  Nevertheless  as  they 
did  not  yield  half  the  number  of  seeds  compared  with 
the  other  flowers  on  the  same  plant  which  had  been 
artificially  and  legitimately  fertilised,  and  as  the  short- 
styled  plants  of  the  two  previous  species  apparently 


100     HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 

evince  some  slight  capacity  for  fertilisation  with  their 
own-form  pollen,  these  three  capsules  may  have  been 
the  product  of  self-fertilisation. 

Besides  the  three  species  now  described,  the  yellow- 
flowered  L.  corymbiferum  is  certainly  heterostyled, 
as  is,  according  to  Planchon,*  L.  salsoloidcs.  This 
botanist  is  the  only  one  who  seems  to  have  inferred 
that  heterostylism  might  have  some  important  func- 
tional bearing.  Dr.  Alefeld,  who  has  made  a  special 
study  of  the  genus,  saysf  that  about  half  of  the  sixty- 
five  species  known  to  him  are  heterostyled.  This  is 
the  case  with  L.  trigynum,  which  differs  so  much  from 
the  other  species  that  it  has  been  formed  by  him  into 
a  distinct  genus.  J  According  to  the  same  author,  none 
of  the  species  which  inhabit  America  and  the  Cape  of 
Good  Hope  are  heterostyled. 

I  have  examined  only  three  homostyled  species, 
namely,  L.  usitatissimum,,  angustifolium,  and  catharti- 
cum.  I  raised  111  plants  of  a  variety  of  the  first-named 
species,  and  these,  when  protected  under  a  net,  all 
produced  plenty  of  seed.  The  flowers,  according  to 
H.  Miiller,§  are  frequented  by  bees  and  moths.  With 
respect  to  L.  catharticum,  the  same  author  shows  that 
the  flowers  are  so  constructed  that  they  can  freely 
fertilise  themselves;  but  if  visited  by  insects  they 
might  be  cross-fertilised.  He  has,  however,  only  once 
seen  the  flowers  thus  visited  during  the  day;  but  it  may 
be  suspected  that  they  are  frequented  during  the  night 
by  small  moths  for  the  sake  of  the  five  minute  drops 


*  Hooker's  'London  Journal  of  Journal  of  Botany,'  1848,  vol.  vii. 

Botany,'  1848,  vol.  vii.  p.  174.  p.     525)    to    be     provided     with 

t 'Bot.  Zeitung,'  Sept.  18,1863,  staminibus  cxsertis;"    another 

p.  281.  with  "  stylis  staminibus  longiori- 

I  It  is  not  improbable  that  the  bus,"  and  another  has  stamina  5, 

allied  genus,  Hugonia,  is  hetero-  majora.  stylos  longe  superantia." 

styled,  for  one  species  is  said  by  \  '  Die    Befruchtung    der    Blu- 

Planchon      (Hooker's     'London  men,' &c.,  p.  168. 


CHAP.  III.          PULMONARIA  OFFICINALIS.  101 

of  nectar  secreted.  Lastly,  L.  Lewisii  is  said  by  Plan- 
chon  to  bear  on  the  same  plant  flowers  with  stamens 
and  pistils  of  the  same  height,  and  others  with  the  pistils 
either  longer  or  shorter  than  the  stamens.  This  case 
formerly  appeared  to  me  an  extraordinary  one;  but  I 
am  now  inclined  to  believe  that  it  is  one  merely  of 
great  variability.* 


PULMONARIA  ( 

Pulmonaria  ofjlcinalis.  —  Hildebrand  has  published  f 
a  full  account  of  this  heterostyled  plant.  The  pistil 
of  the  long-styled  form  is  twice  as  long  as  that  of  the 
short-styled  ;  and  the  stamens  differ  in  a  corresponding, 
though  converse,  manner.  There  is  no  marked  dif- 
ference in  the  shape  or  state  of  surface  of  the  stigma 
in  the  two  forms.  The  pollen-grains  of  the  short- 
styled  form  are  to  those  of  the  long-styled  as  9  to  7, 
or  as  100  to  78,  in  length,  and  as  7  to  6  in  breadth. 
They  do  not  differ  in  the  appearance  of  their  contents. 
The  corolla  of  the  one  form  differs  in  shape  from  that 
of  the  other  in  nearly  the  same  manner  as  in  Primula; 
but  besides  this  difference  the  flowers  of  the  short- 
styled  are  generally  the  larger  of  the  two.  Hilde- 
brand collected  on  the  Siebengebirge,  ten  wild  long- 
styled  and  ten  short-styled  plants.  The  former  bore 
289  flowers,  of  which  186  (i.e.  64  per  cent.)  had  set 
fruit,  yielding  1.88  seed  per  fruit.  The  ten  short- 
styled  plants  bore  373  flowers,  of  which  262  (i.  e. 
70  per  cent.)  had  set  fruit,  yielding  1.86  seed  per 
fruit.  So  that  the  short-styled  plants  produced  many 
more  flowers,  and  these  set  a  rather  larger  proportion 


*  Planchon,  in  Hooker's  '  Lon-  of  Science,'  vol.  xxxvi.,  Sept.,  1863, 

don  Journal  of  Botany,'  1848,  vol.  p.  284. 

vii.  p.  175.    See  on  this  subject  t  '  Bot.  Zeitung,'  1865,  Jan.  13, 

Asa  Gray,  in  '  American  Journal  p.  13. 


102     HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 


of  fruit,  but  the  fruits  themselves  yielded  a  slightly 
lower  average  number  of  seeds  than  did  the  long-styled 
plants.  The  results  of  Hildebrand's  experiments  on 
the  fertility  of  the  two  forms  are  given  in  the  follow- 
ing table : — 

TABLE  19. 
Pulmonaria,  officinalis  (from  Hildebrand). 


Number 

Number 

Nature  of  Union. 

of 
Flowers 

of 
Fruits 

Number  of 
Seeds  per 

fertilised. 

produced. 

Fruit. 

Long-styled  flowers,  by  pollen  of  short-  1 
styled.     Legitimate  union    J 

14 

10 

1.30 

Long-styled  flowers,    14  by  own  pollen,  ] 

and  16  by  pollen  of  other  plant  of  same  > 

30 

0 

0 

form.     Illegitimate  union    J 

Short-styled  flowers,   by  pollen  of  long-  ) 
styled.     Legitimate  union    J 

16 

14 

1.57 

Short-styled  flowers,  11  by  own  pollen,  14  ] 

by  pollen  of  other  plant  of  same  form.  > 

25 

0 

0 

In  the  summer  of  1864,  before  I  had  heard  of  Hilde- 
brand's experiments,  I  noticed  some  long-styled  plants 
of  this  species  (named  for  me  by  Dr.  Hooker)  growing 
by  themselves  in  a  garden  in  Surrey;  and  to  my  sur- 
prise about  half  the  flowers  had  set  fruit,  several  of 
which  contained  2,  and  one  contained  even  3  seeds. 
These  seeds  were  sown  in  my  garden,  and  eleven 
seedlings  thus  raised,  all  of  which  proved  long-styled, 
in  accordance  with  the  usual  rule  in  such  cases.  Two 
years  afterwards  the  plants  were  left  uncovered,  no 
other  plant  of  the  same  genus  growing  in  my  garden, 
and  the  flowers  were  visited  by  many  bees.  They  set 
an  abundance  of  seeds :  for  instance,  I  gathered  from  a 
single  plant  rather  less  than  half  of  the  seeds  which  it 
had  produced,  and  they  numbered  47.  Therefore  this 


CHAP.  III.          PULMONARIA  OFFICINALIS.  103 

illegitimately  fertilised  plant  must  have  produced  about 
100  seeds;  that  is,  thrice  as  many  as  one  of  the  wild 
long-styled  plants  collected  on  the  Siebengebirge  by 
Hildebrand,  and  which,,  no  doubt,  had  been  legitimately 
fertilised.  In  the  following  year  one  of  my  plants 
was  covered  by  a  net,  and  even  under  these  un- 
favourable conditions  it  produced  spontaneously  a 
few  seeds.  It  should  be  observed  that  as  the  flowers 
stand  either  almost  horizontally  or  hang  considerably 
downwards,  pollen  from  the  short  stamens  would  be 
likely  to  fall  on  the  stigma.  We  thus  see  that  the 
English  long-styled  plants  when  illegitimately  ferti- 
lised were  highly  fertile,  whilst  the  German  plants 
similarly  treated  by  Hildebrand  were  completely 
sterile.  How  to  account  for  this  wide  discordance  in 
our  results  I  know  not.  Hildebrand  cultivated  his 
plants  in  pots  and  kept  them  for  a  time  in  the  house, 
whilst  mine  were  grown  out  of  doors;  and  he  thinks 
that  this  difference  of  treatment  may  have  caused  the 
difference  in  our  results.  But  this  does  not  appear  to 
me  nearly  a  sufficient  cause,  although  his  plants  were 
slightly  less  productive  than  the  wild  ones  growing 
on  the  Siebengebirge.  My  plants  exhibited  no  ten- 
dency to  become  equal-styled,  so  as  to  lose  their  proper 
long-styled  character,  as  not  rarely  happens  under 
cultivation  with  several  heterostyled  species  of  Pri- 
mula; but  it  would  appear  that  they  had  been  greatly 
affected  in  function,  either  by  long-continued  cultiva- 
tion or  by  some  other  cause.  We  shall  see  in  a 
future  chapter  that  heterostyled  plants  illegitimately 
fertilised  during  several  successive  generations  some- 
times become  more  self-f ertile ;  and  this  may  have  been 
the  case  with  my  stock  of  the  present  species  of  Pul- 
monaria;  but  in  this  case  we  must  assume  that  the 
long-styled  plants  were  at  first  sufficiently  fertile  to 


104    HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

yield  some  seed,  instead  of  being  absolutely  self-sterile 
like  the  German  plants. 

Pulmonaria  angustifolia. — Seedlings  of  this  plant, 
raised  from  plants  growing  wild  in  the  Isle  of  Wight, 
were  named  for  me  by  Dr.  Hooker.  It  is  so  closely 
allied  to  the  last  species,  differing  chiefly  in  the  shape 
and  spotting  of  the  leaves,  that  the  two  have  been  con- 
sidered by  several  eminent  botanists — for  instance, 
Bentham — as  mere  varieties.  But,  as  we  shall  presently 
see,  good  evidence  can  be  assigned  for  ranking  them 
as  distinct.  Owing  to  the  doubts  on  this  head,  I  tried 
whether  the  two  would  mutually  fertilise  one  another. 
Twelve  short-styled  flowers  of  P.  angustifolia  were 
legitimately  fertilised  with  pollen  from  long-styled 
plants  of  P.  officinalis  (which,  as  we  have  just  seen, 
are  moderately  self -fertile),  but  they  did  not  produce 
a  single  fruit.  Thirty-six  long-styled  flowers  of  P. 
angustifolia  were  also  illegitimately  fertilised  during 
two  seasons  with  pollen  from  the  long-styled  P. 
officinalis,  but  all  these  flowers  dropped  off  unim- 
pregnated.  Had  the  plants  been  mere  varieties  of 
the  same  species  these  illegitimate  crosses  would 
probably  have  yielded  some  seeds,  judging  from  my 
success  in  illegitimately  fertilising  the  long-styled 
flowers  of  P.  officinalis;  and  the  twelve  legitimate 
crosses,  instead  of  yielding  no  fruit,  would  almost  cer- 
tainly have  yielded  a  considerable  number,  namely, 
about  nine,  judging  from  the  results  given  in  the  fol- 
lowing table  (20).  Therefore  P.  officinalis  and  angus- 
tifolia appear  to  be  good  and  distinct  species,  in  con- 
formity with  other  important  functional  differences  be- 
tween them,  immediately  to  be  described. 

The  long-styled  and  short-styled  flowers  of  P.  angus- 
tifolia differ  from  one  another  in  structure  in  nearly 
the  same  manner  as  those  of  P.  officinalis.  But  in  the 


CHAP.  III.        PULMONAEIA  ANGUSTIFOLIA.  105 

accompanying  figure  a  slight  bulging  of  the  corolla 
in  the  long-styled  form,  where  the  anthers  are  seated, 
has  been  overlooked.  My  son  William,  who  examined 
a  large  number  of  wild  plants  in  the  Isle,  of  Wight, 
observed  that  tho  corolla,  though  variable  in  size,  was 
generally  larger  in  the  long-styled  flowers  than  in  the 

Fig.  6. 


Long-styled  form.  Short-styled  form. 

PtJLMONABIA  ANGUSTIFOLIA. 

short-styled;  and  certainly  the  largest  corollas  of  all 
were  found  on  the  long-styled  plants,  and  the  smallest 
on  the  short-styled.  Exactly  the  reverse  occurs,  ac- 
cording to  Hildebrand,  with  P.  officinalis.  Both  the 
pistils  and  stamens  of  P.  angustifolia  vary  much  in 
length;  so  that  in  the  short-styled  form  the  distance 
between  the  stigma  and  the  anthers  varied  from  119 
to  65  divisions  of  the  micrometer,  and  in  the  long- 
styled  form  115  to  112.  From  an  average  of  seven 
measurements  of  each  form  the  distance  between  these 
organs  in  the  long-styled  is  to  the  same  distance  in 
the  short-styled  form  as  100  to  69;  so  that  the  stigma 
in  the  one  form  does  not  stand  on  a  level  with  the 
anthers  in  the  other.  The  long-styled  pistil  is  some- 


106     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

times  thrice  as  long  as  that  of  the  short-styled;  but 
from  an  average  of  ten  measurements  of  both,  its 
length  to  that  of  the  short-styled  was  as  100  to  56. 
The  stigma  varies  in  being  more  or  less,  though 
slightly,  lobed.  The  anthers  also  vary  much  in 
length  in  both  forms,  but  in  a  greater  degree  in  the 
long-styled  than  in  the  short-styled  form;  many  in 
the  former  being  from  80  to  63,  and  in  the  latter 
from  80  to  70  divisions  of  the  micrometer  in  length. 
From  an  average  of  seven  measurements,  the  short- 
styled  anthers  were  to  those  from  the  long-styled  as 
100  to  91  in  length.  Lastly,  the  pollen-grains  from 
the  long-styled  flowers  varied  between  13  and  11.5 
divisions  of  the  micrometer,  and  those  from  the  short- 
styled  between  15  and  13.  The  average  diameter  of 
25  grains  from  the  latter,  or  short-styled  form,  was 
to  that  of  20  grains  from  the  long-styled  as  100  to 
91.  We  see,  therefore,  that  the  pollen-grains  from 
the  smaller  anthers  of  the  shorter  stamens  in  the  long- 
styled  form  are,  as  usual,  of  smaller  size  than  those 
in  the  other  form.  But  what  is  remarkable,  a  larger 
proportion  of  the  grains  were  small,  shrivelled,  and 
worthless.  This  could  be  seen  by  merely  comparing 
the  contents  of  the  anthers  from  several  distinct  plants 
of  each  form.  But  in  one  instance  my  son  found,  by 
counting,  that  out  of  193  grains  from  a  long-styled 
flower,  53  were  bad,  or  27  per  cent.;  whilst  out  of 
265  grains  from  a  short-styled  flower  only  18  were 
bad,  or  7  per  cent.  From  the  condition  of  the  pollen 
in  the  long-styled  form,  and  from  the  extreme  varia- 
bility of  all  the  organs  in  both  forms,  we  may  perhaps 
suspect  that  the  plant  is  undergoing  a  change,  and 
tending  to  become  dioecious. 

My  son  collected  in  the  Isle  of  Wight  on  two  occa- 
sions 202  plants,  of  which  125  were  long-styled  and 


CHAP.  III.        PULMONARIA  ANGUSTIFOLIA. 


107 


77  short-styled;  so  that  the  former  were  the  more 
numerous.  On  the  other  hand,  out  of  18  plants  raised 
by  me  from  seed,  only  4  were  long-styled  and  14 
short-styled.  The  short-styled  plants  seemed  to  my 
son  to  produce  a  greater  number  of  flowers  than  the 
long-styled;  and  he  came  to  this  conclusion  before  a 
similar  statement  had  been  published  by  Hildebrand 
with  respect  to  P.  officinalis.  My  son  gathered  ten 
branches  from  ten  different  plants  of  both  forms,  and 
found  the  number  of  flowers  of  the  two  forms  to  be  as 
100  to  89,  190  being  short-styled  and  169  long-styled. 
With  P.  officinalis  the  difference,  according  to  Hilde- 
brand, is  even  greater,  namely,  as  100  flowers  for  the 
short-styled  to  77  for  the  long-styled  plants.  The 
following  table  shows  the  results  of  my  experi- 
ments : — 

TABLE  20. 
Pulmonaria  angustifolia. 


Nature  of  Union. 

Number 
of 
Flowers 

fertilised. 

Number 
of 
Fruits 
produced. 

Average 

Numbefof 
Seeds  per 
Fruit. 

Long-styled  flowers,  by  pollen  of  short-  I 
styled.     Legitimate  union    J 

18 

9 

2.11 

Long-styled  flowers,  by  own-form  pollen.  1 

18 

0 

0 

Short-styled  flowers,  by  pollen  of  long-  1 
styled.     Legitimate  union    j 

„ 

15 

2.60 

Short-styled  flowers,  by  own-form  pollen.  ) 

12 

7 

1.86 

We  see  in  this  table  that  the  fertility  of  the  two 
legitimate  unions  to  that  of  the  two  illegitimate  to- 
gether is  as  100  to  35,  judged  by  the  proportion  of 
flowers  which  produced  fruit :  and  as  100  to  32,  judged 
by  the  average  number  of  seeds  per  fruit.  But  the 
small  number  of  fruit  yielded  by  the  18  long-styled 


108     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

flowers  in  the  first  line  was  probably  accidental,  and 
if  so,  the  difference  in  the  proportion  of  legitimately 
and  illegitimately  fertilised  flowers  which  yield  fruit 
is  really  greater  than  that  represented  by  the  ratio  of 
100  to  35.  The  18  long-styled  flowers  illegitimately 
fertilised  yielded  no  seeds, — not  even  a  vestige  of  one. 
Two  long-styled  plants  which  were  placed  under  a  net 
produced  138  flowers,  besides  those  which  were  arti- 
ficially fertilised,  and  none  of  these  set  any  fruit;  nor 
did  some  plants  of  the  same  form  which  were  pro- 
tected during  the  next  summer.  Two  other  long- 
styled  plants  were  left  uncovered  (all  the  short-styled 
plants  having  been  previously  covered  up),  and 
humble-bees,  which  had  their  foreheads  white  with 
pollen,  incessantly  visited  the  flowers,  so  that  their 
stigmas  must  have  received  an  abundance  of  pollen, 
yet  these  flowers  did  not  produce  a  single  fruit.  We 
may  therefore  conclude  that  the  long-styled  plants  are 
absolutely  barren  with  their  own-form  pollen,  though 
brought  from  a  distinct  plant.  In  this  respect  they 
differ  greatly  from  the  long-styled  English  plants  of 
P.  officinalis,  which  were  found  by  me  to  be  moderate- 
ly self-f ertile ;  but  they  agree  in  their  behaviour  with 
the  German  plants  of  P.  officinalis  experimented  on  by 
Hildebrand. 

Eighteen  short-styled  flowers  legitimately  fertilised 
yielded,  as  may  be  seen  in  Table  20,  15  fruits,  each 
having  on  an  average  2.6  seeds.  Four  of  these  fruits 
contained  the  highest  possible  number  of  seeds,  namely 
4,  and  four  other  fruits  contained  each  3  seeds.  The 
12  illegitimately  fertilised  short-styled  flowers  yielded 
7  fruits,  including  on  an  average  1.86  seed;  and  one 
of  these  fruits  contained  the  maximum  number  of 
4  seeds.  This  result  is  very  surprising  in  contrast 
with  the  absolute  barrenness  of  the  long-styled  flowers 


CHAP.  III.        PULMONARIA  ANGUSTIPOLIA.  109 

when  illegitimately  fertilised;  and  I  was  thus  led  to 
attend  carefully  to  the  degree  of  self-fertility  of  the 
short-styled  plants.  A  plant  belonging  to  this  form  and 
covered  by  the  net  bore  28  flowers  besides  those  which 
had  been  artificially  fertilised,  and  of  all  these  only 
two  produced  a  fruit  each  including  a  single  seed.  This 
high  degree  of  self-sterility  no  doubt  depended  merely 
on  the  stigmas  not  receiving  any  pollen  or  not  a  suffi- 
cient quantity.  For  after  carefully  covering  all  the 
long-styled  plants  in  my  garden,  several  short-styled 
plants  were  left  exposed  to  the  visits  of  humble-bees, 
and  their  stigmas  will  thus  have  received  plenty  of 
short-styled  pollen;  and  now  about  half  the  flowers, 
vthus  illegitimately  fertilised  set  fruit.  I  judge  of  this 
proportion  partly  from  estimation  and  partly  from 
having  examined  three  large  branches,  which  had  borne 
31  flowers,  and  these  produced  16  fruits.  Of  the  fruits 
produced  233  were  collected  (many  being  left  un- 
gathered),  and  these  included  on  an  average  1.82  seed. 
No  less  than  16  out  of  the  233  fruits  included  the  high- 
est possible  number  of  seeds,  namely  4,  and  31  included 
3  seeds.  So  we  see  how  highly  fertile  these  short- 
styled  plants  were  when  illegitimately  fertilised  with 
their  own-form  pollen  by  the  aid  of  bees. 

The  great  difference  in  the  fertility  of  the  long-. and 
short-styled  flowers,  when  both  are  illegitimately  fer- 
tilised, is  a  unique  case,  as  far  as  I  have  observed,  with 
heterostyled  plants.  The  long-styled  flowers  when  thus 
fertilised  are  utterly  barren,  whilst  about  half  of  the 
short-styled  ones  produce  capsules,  and  these  include  a 
little  above  two-thirds  of  the  number  of  seeds  yielded 
by  them  when  legitimately  fertilised.  The  sterility  of 
the  illegitimately  fertilised  long-styled  flowers  is  prob- 
ably increased  by  the  deteriorated  condition  of  their 
pollen;  nevertheless  this  pollen  was  highly  efficient 


HO     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

when  applied  to  the  stigmas  of  the  short-styled  flowers. 
With  several  species  of  Primula  the  short-styled 
flowers  are  much  more  sterile  than  the  long-styled, 
when  both  are  illegitimately  fertilised;  and  it  is  a 
tempting  view,  as  formerly  remarked,  that  this  greater 
sterility  of  the  short-styled  flowers  is  a  special  adapta- 
tion to  check  self-fertilisation,  as  their  stigmas  are 
eminently  liable  to  receive  their  own  pollen.  This  view 
is  even  still  more  tempting  in  the  case  of  the  long- 
styled  form  of  Linum  grandiflorum.  On  the  other  hand, 
with  Pulmonaria  angustifolia,  it  is  evident,  from  the 
corolla  projecting  obliquely  upwards,  that  pollen  is 
much  more  likely  to  fall  on,  or  to  be  carried  by  insects 
down  to,  the  stigma  of  the  short-styled  than  of  the 
long-styled  flowers ;  yet  the  short-styled,  instead  of  being 
more  sterile,  as  a  protection  against  self-fertilisation, 
are  far  more  fertile  than  the  long-styled,  when  both 
are  illegitimately  fertilised. 

Pulmonaria  azurea,  according  to  Hildebrand,  is  not 
heterostyled.* 

From  an  examination  of  dried  flowers  of  Amsinclcia 
spectabilis,  sent  me  by  Professor  Asa  Gray,  I  formerly 
thought  that  this  plant,  a  member  of  the  Boraginese,  was 
heterostyled.  The  pistil  varies  to  an  extraordinary  degree  in 
length,  being  in  some  specimens  twice  as  long  as  in  others, 
and  the  point  of  insertion  of  the  stamens  likewise  varies. 
But  on  raising  many  plants  from  seed,  I  soon  became  con- 
vinced that  the  whole  case  was  one  of  mere  variability.  The 
first-formed  flowers  are  apt  to  have  stamens  somewhat  ar- 
rested in  development  with  very  little  pollen  in  their  an- 
thers; and  in  such  flowers  the  stigma  projects  above  the 
anthers,  whilst  generally  it  stands  below  and  sometimes 
on  a  level  with  them.  I  could  detect  no  difference  in  the 
size  of  the  pollen-grain  or  in  the  structure  of  the  stigma 
in  the  plants  which  differed  most  in  the  above  respects ;  and 


*  'Die  Gesclilcchter-Vertheilung  bei  den  Pflanzen,'  1867,  p.  37. 


CHAP.  III.  POLYGONUM  FAGOPYRUM.  HI 

all  of  them,  when  protected  from  the  access  of  insects, 
yielded  plenty  of  seeds.  Again,  from  statements  made  by 
Vaucher,  and  from  a  hasty  inspection,  I  thought  at  first 
that  the  allied  Anchusa  arvensis  and  Echium  vulgare  were 
heterostyled,  but  soon  saw  my  error.  From  information 
given  me,  I  examined  dried  flowers  of  another  member  of 
the  Boraginese,  Arnebia  hispidissima,  collected  from  sev- 
eral sites,  and  though  the  corolla,  together  with  the  in- 
cluded organs,  differed  much  in  length,  there  was  no  sign 
of  heterostylism. 

POLYGONUM  FAGOPYRUM    (  POLYGON  ACE.E). 

Hildebrand  has  shown  that  this  plant,  the  common 
Buck- wheat,  is  heterostyled.*  In  the  long-styled  form 
(Fig.  7),  the  three  stigmas  project  considerably  above 
the  eight  short  stamens,  and  stand  on  a  level  with  the 
anthers  of  the  eight  long  stamens  in  the  short-styled 
form;  and  so  it  is  conversely  with  the  stigmas  and 
stamens  of  this  latter  form.  I  could  perceive  no  differ- 
ence in  the  structure  of  the  stigmas  in  the  two  forms. 
The  pollen-grains  of  the  short-styled  form  are  to  those 
of  the  long-styled  as  100  to  82  in  diameter.  This  plant 
is  therefore  without  doubt  heterostyled. 

I  experimented  only  in  an  imperfect  manner  on  the 
relative  fertility  of  the  two  forms.  Short-styled  flowers 
were  dragged  several  times  over  two  heads  of  flowers 
on  long-styled  plants,  protected  under  a  net,  which  were 
thus  legitimately,  though  not  fully,  fertilised.  They 
produced  22  seeds,  or  11  per  flower-head. 

Three  flower-heads  on  long-styled  plants  received 
pollen  in  the  same  manner  from  other  long-styled  plants, 
and  were  thus  illegitimately  fertilised.  They  produced 
14  seeds,  or  only  4.66  per  flower-head. 

Two  flower-heads  on  short-styled  plants  received 
pollen  in  like  manner  from  long-styled  flowers,  and 


*  '  Die  Geschlechter-Vertheilung,'  &c.,  1867,  p.  34. 


112     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

were   thus   legitimately   fertilised.     They  produced   8 
seeds,  or  4  per  flower-head. 

Four  heads  on  short-styled  plants  similarly  received 
pollen  from  other  short-styled  plants,  and  were  thus 

Fig.  7. 


Upper  figure,  the  long-styled  form ;  lower  figure,  the  short-styled. 
Some  of  the  anthers  have  dehisced,  others  have  not. 

POLYGONUM  FAGOPYEUM.     (From  H.  Miiller.) 


illegitimately  fertilised.     They  produced  9  seeds,  or  2.25 
per  flower-head. 

The  result  from  fertilising  the  flower-heads  in  the 
above  imperfect  manner  cannot  be  fully  trusted;  but 
I  may  state  that  the  four  legitimately  fertilised  flower- 
heads  yielded  on  an  average  7.50  seeds  per  head; 
whereas  the  seven  illegitimately  fertilised  heads 
yielded  less  than  half  the  number,  or  on  an  average 
only  3.28  seeds.  The  legitimately  crossed  seeds  from 
the  long-styled  flowers  were  finer  than  those  from  the 


CHAP.  III.  POLYGONUM  FAGOPYRTJM.  H3 

illegitimately  fertilised  flowers  on  the  same  plants,  in 
the  ratio  of  100  to  82,  as  shown  by  the  weights  of  an 
equal  number. 

About  a  dozen  plants,  including  both  forms,  were 
protected  under  nets,  and  early  in  the  season  they  pro- 
duced spontaneously  hardly  any  seeds,  though  at  this 
period  the  artificially  fertilised  flowers  produced  an 
abundance;  but  it  is  a  remarkable  fact  that  later  in 
the  season,  during  September,  both  forms  became  highly 
self-fertile.  They  did  not,  however,  produce  so  many 
seeds  as  some  neighbouring  uncovered  plants  which 
were  visited  by  insects.  Therefore  the  flowers  of  neither 
form,  when  left  to  fertilise  themselves  late  in  the  season 
without  the  aid  of  insects,  are  nearly  so  sterile  as  most 
other  heterostyled  plants.  A  large  number  of  insects, 
namely,  41  kinds  as  observed  by  H.  Miiller,*  visit  the 
flowers  for  the  sake  of  the  eight  drops  of  nectar.  He 
infers  from  the  structure  of  the  flowers  that  insects 
would  be  apt  to  fertilise  them  both  illegitimately  as 
well  as  legitimately;  but  he  is  mistaken  in  supposing 
that  the  long-styled  flowers  cannot  spontaneously  fer- 
tilise themselves. 

Differently  to  what  occurs  in  the  other  genera 
hitherto  noticed,  Polygonum,  though  a  very  large 
genus,  contains,  as  far  as  is  at  present  known,  only  a 
single  heterostyled  species,  namely,  the  present  one. 
H.  Miiller,  in  his  interesting  description  of  several 
other  species,  shows  that  P.  bistorta  is  so  strongly  pro- 
terandrous  (the  anthers  generally  falling  off  before  the 
stigmas  are  mature)  that  the  flowers  must  be  cross- 
fertilised  by  the  many  insects  which  visit  them.  Other 
species  bear  much  less  conspicuous  flowers  which  se- 
crete little  or  no  nectar,  and  consequently  are  rarely 


*  'Die  Befruchtung,'  &c.,  p.  175,  and  'Nature,'  January  1,  1874, 
p.  166. 


114:     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

visited  by  insects;  these  are  adapted  for  self -fertilisa- 
tion, though  still  capable  of  cross-fertilisation.  Ac- 
cording to  Delpino,  the  Polygonaceae  are  generally 
fertilised  by  the  wind,  instead  of  by  insects  as  in  the 
present  genus. 

LEUCOSMIA  BURNETTIANA  (THYMELLE). 

As  Professor  Asa  Gray  has  expressed  his  belief  *  that 
this  species  and  L.  acuminata,  as  well  as  some  species  in 
the  allied  genus  Drymispermum,  are  dimorphic  or  hetero- 
styled,  I  procured  from  Kew,  through  the  kindness  of  Dr. 
Hooker,  two  dried  flowers  of  the  former  species,  an  in- 
habitant of  the  Friendly  Islands  in  the  Pacific.  The  pistil 
of  the  long-styled  form  is  to  that  of  the  short-styled  as  100 
to  86  in  length;  the  stigma  projects  just  above  the  threat 
of  the  corolla,  and  is  surrounded  by  five  anthers,  the  tips 
of  which  reach  up  almost  to  its  base;  and  lower  down, 
within  the  tubular  corolla,  five  other  and  rather  smaller 
anthers  are  seated.  In  the  short-styled  form,  the  stigma 
stands  some  way  down  the  tube  of  the  corolla,  nearly  on  a 
level  with  the  lower  anthers  of  the  other  form:  it  differs 
remarkably  from  the  stigma  of  the  long-styled  form,  in 
being  more  papillose,  and  in  being  longer  in  the  ratio  of 
100  to  60.  The  anthers  of  the  upper  stamens  in  the  short- 
styled  form  are  supported  on  free  filaments,  and  project 
above  the  throat  of  the  corolla,  whilst  the  anthers  of  the 
lower  stamens  are  seated  in  the  throat  on  a  level  with  the 
upper  stamens  of  the  other  form.  The  diameters  of  a  con- 
siderable number  of  grains  from  both  sets  of  anthers  in 
both  forms  were  measured,  but  they  did  not  differ  in  any 
trustworthy  degree.  The  mean  diameter  of  twenty-two 
grains  from  the  short-styled  flower  was  to  that  of  twenty- 
four  grains  from  the  long-styled,  as  100  to  99.  The  anthers 
of  the  upper  stamens  in  the  short-styled  form  appeared  to 
be  poorly  developed,  and  contained  a  considerable  number 
of  shrivelled  grains  which  were  omitted  in  striking  the 
above  average.  Notwithstanding  the  fact  of  the  pollen- 


*  'American    Journal    of  Sci-     'Journal     of   Botany,'    vol.    iii., 
ence,'  1865,  p.  101,  and  Seemann's     1865,  p.  305. 


CHAP.  III.          MENYANTHES  TRIFOLIATA.  H5 

grains  from  the  two  forms  not  differing  in  diameter  in  any 
appreciable  degree,  there  can  hardly  be  a  doubt  from  the 
great  difference  in  the  two  forms  in  the  length  of  the  pistil, 
and  especially  of  the  stigma,  together  with  its  more  papil- 
lose condition  in  the  short-styled  form,  that  the  present  spe- 
cies is  truly  heterostyled.  This  case  resembles  that  of 
Linum  grandiflorum,  in  which  the  sole  difference  between 
the  two  forms  consists  in  the  length  of  the  pistils  and  stig- 
mas. From  the  great  length  of  the  tubular  corolla  of  Leu- 
cosmia,  it  is  clear  that  the  flowers  are  cross-fertilised  by 
large  Lepidoptera  or  by  honey-sucking  birds,  and  the  posi- 
tion of  the  stamens  in  two  whorls  one  beneath  the  other, 
which  is  a  character  that  I  have  not  seen  in  any  other 
heterostyled  dimorphic  plant,  probably  serves  to  smear  the 
inserted  organ  thoroughly  with  pollen. 

MENYANTHES  TRIFOLIATA  (GENTIANEJE). 

This  plant  inhabits  marshes :  my  son  William  gathered 
247  flowers  from  so  many  distinct  plants,  and  of  these  110 
were  long-styled,  and  137  short-styled.  The  pistil  of  the 
long-styled  form  is  in  length  to  that  of  the  short-styled  in 
the  ratio  of  about  3  to  2.  The  stigma  of  the  former,  as 
my  son  observed,  is  decidedly  larger  than  that  of  the  short- 
styled;  but  in  both  forms  it  varies  much  in  size.  The 
stamens  of  the  short-styled  are  almost  double  the  length  of 
those  of  the  long-styled ;  so  that  their  anthers  stand  rather 
above  the  level  of  the  stigma  of  the  long-styled  form.  The 
anthers  also  vary  much  in  size,  but  seem  often  to  be  of 
larger  size  in  the  short-styled  flowers.  My  son  made  with 
the  camera  many  drawings  of  the  pollen-grains,  and  those 
from  the  short-styled  flowers  were  in  diameter  in  nearly  the 
ratio  of  100  to  84  to  those  from  the  long-styled  flowers.  I 
know  nothing  about  the  capacity  for  fertilisation  in  the 
two  forms;  but  short-styled  plants,  living  by  themselves 
in  the  gardens  at  Kew,  have  produced  an  abundance  of  cap- 
sules, yet  the  seeds  have  never  germinated;  and  this  looks 
as  if  the  short-styled  form  was  sterile  with  its  own  pollen. 

LlMNANTHEMUM  INDICUM   (GENTIANS^). 

This  plant  is  mentioned  by  Mr.  Thwaites,  in  his  Enu- 
meration of  the  Plants  of  Ceylon,  as  presenting  two  forms ; 


116     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

and  he  was  so  kind  as  to  send  me  specimens  preserved  in 
spirits.  The  pistil  of  the  long-styled  form  is  nearly  thrice 
as  long  (i.  e.  as  14  to  5)  as  that  of  the  short-styled,  and  is 
very  much  thinner  in  the  ratio  of  about  3  to  5.  The  folia- 
ceous  stigma  is  more  expanded,  and  twice  as  large  as  that 
of  the  short-styled  form.  In  the  latter  the  stamens  are 
about  twice  as  long  as  those  of  the  long-styled,  and  their 
anthers  are  larger  in  the  ratio  of  100  to  70.  The  pollen- 
grains,  after  having  been  long  kept  in  spirits,  were  of  the 
same  shape  and  size  in  both  forms.  The  ovules,  according 
to  Mr.  Thwaites,  are  equally  numerous  (viz.  from  70  to 
80)  in  the  two  forms. 

VILLARSIA  [SP.?]  (GENTIANE.E). 

Fritz  Miiller  sent  me  from  South  Brazil  dried  flowers 
of  this  aquatic  plant,  which  is  closely  allied  to  Limnanthe- 
mum.  In  the  long-styled  form  the  stigma  stands  some  way 
above  the  anthers,  and  the  whole  pistil,  together  with 
the  ovary,  is  in  length  to  that  of  the  short-styled  form  as 
about  3  to  2.  In  the  latter  form  the  anthers  stand  above 
the  stigma,  and  the  style  is  very  short  and  thick;  but  the 
pistil  varies  a  good  deal  in  length,  the  stigma  being  either 
on  a  level  with  the  tips  of  the  sepals  or  considerably  be- 
neath them.  The  foliaceous  stigma  in  the  long-styled  form 
is  larger,  with  the  expansions  running  farther  down  the 
style,  than  in  the  other  form.  One  of  the  most  remarkable 
differences  between  the  two  forms  is  that  the  anthers  of 
the  longer  stamens  in  the  short-styled  flowers  are  con- 
spicuously longer  than  those  of  the  shorter  stamens  in  the 
long-styled  flowers.  In  the  former  the  sub-triangular  pol- 
len-grains are  larger;  the  ratio  between  their  breadth 
(measured  from  one  angle  to  the  middle  of  the  opposite 
side)  and  that  of  the  grains  from  the  long-styled  flowers  be- 
ing about  100  to  75.  Fritz  Miiller  also  informs  me  that  the 
pollen  of  the  short-styled  flowers  has  a  bluish  tint,  whilst 
that  of  the  long-styled  is  yellow.  When  we  treat  of  Lyth- 
rum  salicaria  we  shall  find  a  strongly  marked  contrast  in 
the  colour  of  the  pollen  in  two  of  the  forms. 

The  three  genera,  Menyanthes,  Limnanthemum,  and 
Villarsia,  now  described,  constitute  a  well-marked  sub- 
tribe  of  the  Gentianea3.  All  the  species,  as  far  as  at  pres- 


CHAP.  III.  CORDIA.  H? 

ent  known,  are  heterostyled,  and  all  inhabit  aquatic  or  sub- 
aquatic  stations. 

FORSYTHIA  SUSPENSA   (OLEACE^). 

Professor  Asa  Gray  states  that  the  plants  of  this  species 
growing  in  the  Botanic  Gardens  at  Cambridge,  U.  S.,  are 
short-styled,  but  that  Siebold  and  Zuccarini  describe  the 
long-styled  form,  and  give  figures  of  two  forms;  so  that 
there  can  be  little  doubt,  as  he  remarks,  about  the  plant 
being  dimorphic.*  I  therefore  applied  to  Dr.  Hooker,  who 
sent  me  a  dried  flower  from  Japan,  another  from  China, 
and  another  from  the  Botanic  Gardens  at  Kew.  The  first 
proved  to  be  long-styled,  and  the  other  two  short-styled. 
In  the  long-styled  form,  the  pistil  is  in  length  to  that  of  the 
short-styled  as  100  to  38,  the  lobes  of  the  stigma  being  a 
little  longer  (as  10  to  9),  but  narrower  and  less  divergent. 
This  last  character,  however,  may  be  only  a  temporary 
one.  There  seems  to  be  no  difference  in  the  papillose  con- 
dition of  the  two  stigmas.  In  the  short-styled  form,  the 
stamens  are  in  length  to  those  of  the  long-styled  as  100  to 
66,  but  the  anthers  are  shorter  in  the  ratio  of  87  to  100 ;  and 
this  is  unusual,  for  when  there  is  any  difference  in  size 
between  the  anthers  of  the  two  forms,  those  from  the 
longer  stamens  of  the  short-styled  are  generally  the  long- 
est. The  pollen-grains  from  the  short-styled  flowers  are 
certainly  larger,  but  only  in  a  slight  degree,  than  those 
from  the  long-styled,  namely,  as  100  to  94  in  diameter. 
The  short-styled  form-  which  grows  in  the  Gardens  at  Kew 
has  never  there  produced  fruit. 

Forsythia  viridissima  appears  likewise  to  be  hetero- 
styled ;  for  Professor  Asa  Gray  says  that,  although  the  long- 
styled  form  alone  grows  in  the  gardens  at  Cambridge,  U.  S., 
the  published  figures  of  this  species  belong  to  the  short- 
styled  form. 

CORDIA  [SP.?]  (CORDIACE^E.) 

Fritz  Miiller  sent  me  dried  specimens  of  this  shrub, 
which  he  believes  to  be  heterostyled ;  and  I  have  not  much 
doubt  that  this  is  the  case,  though  the  usual  characteristic 


*  '  The  American  Naturalist,'  July,  1873,  p.  422. 


118     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

differences  are  not  well  pronounced  in  the  two  forms. 
Linum  grandiflorum  shows  us  that  a  plant  may  be  hetero- 
styled  in  function  in  the  highest  degree,  and  yet  the  two 
forms  may  have  stamens  of  equal  length,  and  pollen-grains 
of  equal  size.  In  the  present  species  of  Cordia,  the  stamens 
of  both  forms  are  of  nearly  equal  length,  those  of  the  short- 
styled  being  rather  the  longest;  and  the  anthers  of  both 
are  seated  in  the  mouth  of  the  corolla.  Nor  could  I  detect 
any  difference  in  the  size  of  the  pollen-grains,  when  dry  or 
after  being  soaked  in  water.  The  stigmas  of  the  long-styled 
form  stand  clear  above  the  anthers,  and  the  whole  pistil 
is  longer  than  that  of  the  short-styled,  in  about  the  ratio 
of  3  to  2. 

The  stigmas  of  the  short-styled  form  are  seated  be- 
neath the  anthers,  and  they  are  considerably  shorter  than 
those  of  the  long-styled  form.  This  latter  difference  is  the 
most  important  one  of  any  between  the  two  forms. 

GlLIA  (IPOMOPSIS)   PULCHELLA  VEL  AGGREGATA  (PoLEMONI- 
ACE.E). 

Professor  Asa  Gray  remarks  with  respect  to  this  plant : 
"  The  tendency  to  dimorphism,  of  which  there  are  traces, 
or  perhaps  rather  incipient  manifestations  in  various  por- 
tions of  the  genus,  is  most  marked  in  G.  aggregata"  *  He 
sent  me  some  dried  flowers,  and  I  procured  others  from 
Kew.  They  differ  greatly  in  size,  some  being  nearly  twice 
as  long  as  others  (viz.  as  30  to  17),  so  that  it  was  not  pos- 
sible to  compare,  except  by  calculation,  the  absolute  length 
of  the  organs  from  different  plants.  Moreover  the  rela- 
tive position  of  the  stigmas  and  anthers  is  variable:  in 
some  long-styled  flowers  the  stigmas  and  anthers  were  ex- 
serted  only  just  beyond  the  throat  of  the  corolla ;  whilst  in 
others  they  were  exserted  as  much  as  &  of  an  inch.  I  sus- 
pect also  that  the  pistil  goes  on  growing  for  some  time  after 
the  anthers  have  dehisced.  Nevertheless  it  is  possible  to 
class  the  flowers  under  two  forms.  In  some  of  the  long- 
styled,  the  length  of  pistil  to  that  of  the  short-styled  was  as 
100  to  82 ;  but  this  result  was  gained  by  reducing  the  size 
of  the  corollas  to  the  same  scale.  In  another  pair  of 


*  'Proc.  American  Acad.  of  Arts  and  Sciences,'  June  14,  1870, 
p.  275. 


CHAP.  III.  GILIA  MICRANTHA.  119 

flowers  the  difference  in  length  between  the  pistils  of  the 
two  forms  was  certainly  greater,  but  they  were  not  actu- 
ally measured.  In  the  short-styled  flowers,  whether  large 
or  small,  the  stigma  is  seated  low  down  within  the  tube  of 
the  corolla.  The  papillae  on  the  long-styled  stigma  are 
longer  than  those  on  the  short-styled,  in  the  ratio  of  100  to 
40.  The  filaments  in  some  of  the  short-styled  flowers  were, 
to  those  of  the  long-styled,  as  100  to  25  in  length,  the  free, 
or  unattached  portion  being  alone  measured;  but  this 
ratio  cannot  be  trusted,  owing  to  the  great  variability  of 
the  stamens.  The  mean  diameter  of  eleven  pollen-grainy 
from  long-styled  flowers,  and  of  twelve  from  the  short- 
styled,  was  exactly  the  same.  It  follows  from  these  several 
statements,  that  the  difference  in  length  and  state  of  sur- 
face of  the  stigmas  in  the  flowers  is  the  sole  reliable  evi- 
dence that  this  species  is  heterostyled ;  for  it  would  be  rash 
to  trust  to  the  difference  in  the  length  of  the  pistils,  seeing 
how  variable  they  are.  I  should  have  left  the  case  alto- 
gether doubtful,  had  it  not  been  for  the  observations  on  the 
following  species ;  and  these  leave  little  doubt  on  my  mind 
that  the  present  plant  is  truly  heterostyled.  Professor 
Gray  informs  me  that  in  another  species,  G.  coronopifolia, 
belonging  to  the  same  section  of  the  genus,  he  can  see  no 
sign  of  dimorphism. 

GILIA  (LEPTOSIPHON)  MICRANTHA. 

A  few  flowers  sent  me  from  Kew  had  been  somewhat  in- 
jured, so  that  I  cannot  say  anything  positively  with  respect 
to  the  position  and  relative  length  of  the  organs  in  the  two 
forms.  But  their  stigmas  differed  almost  exactly  in  the 
same  manner  as  in  the  last  species ;  the  papillae  on  the  long- 
styled  stigma  being  longer  than  those  on  the  short-styled, 
in  the  ratio  of  100  to  42.  My  son  measured  nine  pollen- 
grains  from  the  long-styled,  and  the  same  number  from  the 
short-styled  form;  and  the  mean  diameter  of  the  former 
was  to  that  of  the  latter  as  100  to  81.  Considering  this  dif- 
ference, as  well  as  that  between  the  stigmas  of  the  two 
forms,  there  can  be  no  doubt  that  this  species  is  hetero- 
styled. So  probably  is  Gilia  nudicaulis,  which  likewise  be- 
longs to  the  Leptosiphon  section  of  the  genus,  for  I  hear 
from  Professor  Asa  Gray  that  in  some  individuals  the 


120     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

style  is  very  long,  with  the  stigma  more  or  less  exserted, 
whilst  in  others  it  is  deeply  included  within  the  tube ;  the 
anthers  being  always  seated  in  the  throat  of  the  corolla. 

PHLOX  SUBULATA  (POLEMONIACE^:). 

Professor  Asa  Gray  informs  me  that  the  greater  number 
of  the  species  in  this  genus  have  a  long  pistil,  with  the 
stigma  more  or  less  exserted;  whilst  several  other  species, 
especially  the  annuals,  have  a  short  pistil  seated  low  down 
within  the  tube  of  the  corolla.  In  all  the  species  the  an- 
thers are  arranged  one  below  the  other,  the  uppermost  just 
protruding  from  the  throat  of  the  corolla.  In  Phlox  subu- 
lata  alone  he  has  "  seen  both  long  and  short  styles ;  and 
here  the  short-styled  plant  has  (irrespective  of  this  char- 
acter) been  described  as  a  distinct  species  (P.  nivalis,  P. 
Hentzii),  and  is  apt  to  have  a  pair  of  ovules  in  each  cell, 
while  the  long-styled  P.  subulata  rarely  shows  more  than 
one."  *  Some  dried  flowers  of  both  forms  were  sent  me  by 
him,  and  I  received  others  froin  Kew,  but  I  have  failed 
to  make  out  whether  the  species  is  heterostyled.  In  two 
flowers  of  nearly  equal  size,  the  pistil  of  the  long-styled 
form  was  twice  as  long  as  that  of  the  short-styled ;  but  in 
other  cases  the  difference  was  not  nearly  so  great.  The 
stigma  of  the  long-styled  pistil  stands  nearly  in  the  throat 
of  the  corolla;  whilst  in  the  short-styled  it  is  placed  low 
down — sometimes  very  low  down  in  the  tube,  for  it  varies 
greatly  in  position.  The  stigma  is  more  papillose,  and  of 
greater  length  (in  one  instance  in  the  ratio  of  100  to  67), 
in  the  short-styled  flowers  than  in  the  long-styled.  My  son 
measured  twenty  pollen-grains  from  a  short-styled  flower, 
and  nine  from  a  long-styled,  and  the  former  were  in  diam- 
eter to  the  latter  as  100  to  93 ;  and  this  difference  accords 
with  the  belief  that  the  plant  is  heterostyled.  But  the 
grains  from  the  short-styled  varied  much  in  diameter.  He 
afterwards  measured  ten  grains  from  a  distinct  long-styled 
flower,  and  ten  from  another  plant  of  the  same  form,  and 
these  grains  differed  in  diameter  in  the  ratio  of  100  to  90. 
The  mean  diameter  of  these  two  lots  of  twenty  grains  was 
to  that  of  twelve  grains  from  another  short-styled  flower 


*  '  Proc.  American  Acad.  of  Arts  and  Sciences,'  June  14, 1870,  p.  248. 


CHAP.  III.  ERYTHROXYLUM.  121 

as  100  to  75 :  here,  then,  the  grains  from  the  short-styled 
form  were  considerably  smaller  than  those  from  the  long- 
styled,  which  is  the  reverse  of  what  occurred  in  the  former 
instance,  and  of  what  is  the  general  rule  with  heterostyled 
plants.  The  whole  case  is  perplexing  in  the  highest  de- 
gree, and  will  not  be  understood  until  experiments  are  tried 
on  living  plants.  The  greater  length  and  more  papillose 
condition  of  the  stigma  in  the  short-styled  than  in  the 
long-styled  flowers,  looks  as  if  the  plant  was  heterostyled; 
for  we  know  that  with  some  species — for  instance,  Leu- 
cosmia  and  certain  Eubiacese — the  stigma  is  longer  and 
more  papillose  in  the  short-styled  form,  though  the  re- 
verse of  this  holds  good  in  Gilia,  a  member  of  the  same 
family  with  Phlox.  The  similar  position  of  the  anthers  in 
the  two  forms  is  somewhat  opposed  to  the  present  species 
being  heterostyled ;  as  is  the  great  difference  in  the  length 
of  the  pistil  in  several  short-styled  flowers.  But  the  ex- 
traordinary variability  in  diameter  of  the  pollen-grains, 
and  the  fact  that  in  one  set  of  flowers  the  grains  from  the 
long-styled  flowers  were  larger  than  those  from  the  short- 
styled,  is  strongly  opposed  to  the  belief  that  Phlox  subulata 
is  heterostyled.  Possibly  this  species  was  once  heterostyled, 
but  is  now  becoming  sub-difficious ;  the  short-styled  plants 
having  been  rendered  more  feminine  in  nature.  This 
would  account  for  their  ovaries  usually  containing  more 
ovules,  and  for  the  variable  condition  of  their  pollen- 
grains.  Whether  the  long-styled  plants  are  now  changing 
their  nature,  as  would  appear  to  be  the  case  from  the  varia- 
bility of  their  pollen-grains,  and  are  becoming  more  mas- 
culine, I  will  not  pretend  to  conjecture;  they  might  re- 
main as  hermaphrodites,  for  the  co-existence  of  herma- 
phrodite and  female  plants  of  the  same  species  is  by  no 
means  a  rare  event. 


ERYTHROXYLUM  [SP.?]  (ERYTHROXYLID.E). 

Fritz  Miiller  sent  me  from  South  Brazil  dried  flowers 
of  this  tree,  together  with  the  accompanying  drawings, 
which  show  the  two  forms,  magnified  about  five  times,  with 
the  petals  removed.  In  the  long-styled  form  the  stigmas 
project  above  the  anthers,  and  the  styles  are  nearly  twice 
as  long  as  those  of  the  short-styled  form,  in  which  the 
10 


122     HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 

stigmas  stand  beneath  the  anthers.  The  stigmas  in  many, 
but  not  in  all  the  short-styled  flowers,  are  larger  than  those 
in  the  long-styled.  The  anthers  of  the  short-styled  flowers 
stand  on  a  level  with  the  stigmas  of  the  other  form;  but 
the  stamens  are  longer  by  only  one-fourth  or  one-nf th  of 

Fig.  8. 


Long-styled  form.  Short  styled  form. 

From  a  sketch  by  Fritz  Miiller,  magnified  five  times. 
EEYTHEOXYLON  [sp.  ?]. 

their  own  length  than  those  of  the  long-styled.  Conse- 
quently the  anthers  of  the  latter  do  not  stand  on  a  level 
with,  but  rather  above  the  stigmas  of  the  other  form.  Dif- 
ferently from  what  occurs  in  the  following  closely  allied 
genus,  Sethia,  the  stamens  are  of  nearly  equal  length  in 
the  flowers  of  the  same  form.  The  pollen-grains  of  the 
short-styled  flowers,  measured  in  their  dry  state,  are  a  little 
larger  than  those  from  the  long-styled  flowers  in  about  the 
ratio  of  100  to  93.* 


*  F.  Miiller  remarks  in  his  let- 
ter to  me  that  the  flowers,  of  which 
he  carefully  examined  many  spe- 
cimens, are  curiously  variable 
in  the  number  of  their  parts  :  5 
sepals  and  petals,  10  stamens  and  3 


pistils  are  the  prevailing  numbers ; 
but  the  sepals  and  petals  often 
vary  from  5  to  7 ;  the  stamens  from 
10  to  14,  and  the  pistils  from 
3  to  4. 


CHAP.  III.  CRATOXYLOX  FORMOSUM.  123 

SETHIA  ACUMINATA  (ERYTHROXYLIOE). 

Mr,  Thwaites  pointed  out  several  years  ago  *  that  this 
plant  exists  under  two  forms,  which  he  designated  as 
forma  stylosa  et  staminea;  and  the  flowers  sent  to  me  by 
him  are  clearly  heterostyled.  In  the  long-styled  form  the 
pistil  is  nearly  twice  as  long,  and  the  stamens  half  as  long 
as  the  corresponding  organs  in  the  short-styled  form.  The 
stigmas  of  the  long-styled  seem  rather  smaller  than  those 
of  the  short-styled.  All  the  stamens  in  the  short-styled 
flowers  are  of  nearly  equal  length,  whereas  in  the  long- 
styled  they  differ  in  length,  being  alternately  a  little  longer 
and  shorter;  and  this  difference  in  the  stamens  of  the  two 
forms  is  probably  related,  as  we  shall  hereafter  see  in  the 
case  of  the  short-styled  flowers  of  Lythrum  salicaria,  to  the 
manner  in  which  insects  can  best  transport  pollen  from 
the  long-styled  flowers  to  the  stigmas  of  the  short-styled. 
The  pollen-grains  from  the  short-styled  flowers,  though 
variable  in  size,  are  to  those  of  the  long-styled,  as  far  as  I 
could  make  out,  as  100  to  83  in  their  longer  diameter. 
Sethia  oltusifolia  is  heterostyled  like  8.  acuminata. 

CRATOXYLON  FORMOSUM  (HYPERICINE^E). 

Mr.  Thiselton  Dyer  remarks  that  this  tree,  an  inhabit- 
ant of  Malacca  and  Borneo,  appears  to  be  heterostyled.  f 
He  sent  me  dried  flowers,  and  the  difference  between  the 
two  forms  is  conspicuous.  In  the  long-styled  form  the 
pistils  are  in  length  to  those  of  the  short-styled  as  100  to 
40,  with  their  globular  stigmas  about  twice  as  thick.  These 
stand  just  above  the  numerous  anthers  and  a  little  beneath 
the  tips  of  the  petals.  In  the  short-styled  form  the  anthers 
project  high  above  the  pistils,  the  stigmas  of  which  diverge 
between  the  three  bundles  of  stamens,  and  stand  only  a 
little  above  the  tips  of  the  sepals.  The  stamens  in  this 
form  are  to  those  of  the  long-styled  as  100  to  86  in  length ; 
and  therefore  they  do  not  differ  so  much  in  length  as  do 
the  pistils.  Ten  pollen-grains  from  each  form  were  meas- 
ured, and  those  from  the  short-styled  were  to  those  from 
the  long-styled  as  100  to  86  in  diameter.  This  plant,  there- 


*  '  Enumeratio  Plantarum  Zcy-        t  'Journal  of  Botany,' London, 
laniae, '  1864,  p.  54.  1872,  p.  26. 


124     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

fore,  is  in  all  respects  a  well-characterised  heterostyled 
species. 

^GIPHILA  ELATA   (VERBENACE^). 

Mr.  Bentham  was  so  kind  as  to  send  me  dried  flowers 
of  this  species  and  of  2E.  mollis,  both  inhabitants  of  South 
America.  The  two  forms  differ  conspicuously,  as  the  deep- 
ly bifid  stigma  of  the  one  and  the  anthers  of  the  other 
project  far  above  the  mouth  of  the  corolla.  In  the  long- 
styled  form  of  the  present  species,  the  style  is  twice  and  a 
half  as  long  as  that  of  the  short-styled.  The  divergent 
stigmas  of  the  two  forms  do  not  differ  much  in  length,  nor 
as  far  as  I  could  perceive  in  their  papillae.  In  the  long- 
styled  flowers  the  filaments  adhere  to  the  corolla  close  up 
to  the  anthers,  which  are  enclosed  some  way  down  within 
the  tube.  In  the  short-styled  flowers  the  filaments  are  free 
above  the  point  where  the  anthers  are  seated  in  the  other 
form,  and  they  project  from  the  corolla  to  an  equal  height 
with  that  of  the  stigmas  in  the  long-styled  flowers.  It  is 
often  difficult  to  measure  with  accuracy  pollen-grains 
which  have  long  been  dried  and  then  soaked  in  water  ;  but 
they  here  manifestly  differed  greatly  in  size.  Those  from 
the  short-styled  flowers  were  to  those  from  the  long-styled 
in  diameter  in  about  the  ratio  of  100  to  62.  The  two  forms 
of  2E.  mollis  present  a  like  difference  in  the  length  of 
their  pistils  and  stamens. 


Flowers  of  this  bush  were  sent  me  from  St.  Catharina 
in  Brazil,  by  Fritz  Miiller,  and  were  named  for  me  at 
Kew.  They  appeared  at  first  sight  grandly  heterostyled, 
as  the  stigma  of  the  long-styled  form  projects  far  out  of 
the  corolla,  whilst  the  anthers  are  seated  halfway  down 
within  the  tube  ;  whereas  in  the  short-styled  form  the  an- 
thers project  from  the  corolla  and  the  stigma  is  enclosed  in 
the  tube  at  nearly  the  same  level  with  the  anthers  of  the 
other  form.  The  pistil  of  the  long-styled  is  to  that  of  the 
short-styled  as  100  to  60  in  length,  and  the  stigmas,  taken 
by  themselves,  as  100  to  55.  Nevertheless  this  plant  cannot 
be  heterostyled.  The  anthers  in  the  long-styled  form  are 
brown,  tough,  and  fleshy,  and  less  than  half  the  length 
of  those  in  the  short-styled  form,  strictly  as  44  to  100;  and, 


CHAP.  III.  MITCHELLA  REPENS.  125 

what  is  much  more  important,  they  were  in  a  rudimentary 
condition  in  the  two  flowers  examined  by  me,  and  did  not 
contain  a  single  grain  of  pollen.  In  the  short-styled  form, 
the  divided  stigma,  which  as  we  have  seen  is  much  short- 
ened, is  thicker  and  more  fleshy  than  the  stigma  of  the  long- 
styled,  and  is  covered  with  small  irregular  projections, 
formed  of  rather  large  cells.  It  had  the  appearance  of  hav- 
ing suffered  from  hypertrophy,  and  is  probably  incapable 
of  fertilisation.  If  this  be  so  the  plant  is  dioecious,  and, 
judging  from  the  two  species  previously  described,  it  proba- 
bly was  once  heterostyled,  and  has  since  been  rendered 
dioecious  by  the  pistil  in  the  one  form*  and  the  stamens  in 
the  other  having  become  functionless  and  reduced  in  size. 
It  is,  however,  possible  that  the  flowers  may  be  in  the  same 
state  as  those  of  the  common  thyme  and  of  several  other 
Labiatse,  in  which  females  and  hermaphrodites  regularly 
coexist.  Fritz  Miiller,  who  thought  that  the  present  plant 
was  heterostyled,  as  I  did  at  first,  informs  me  that  he  found 
bushes  in  several  places  growing  quite  isolated,  and  that 
these  were  completely  sterile;  whilst  two  plants  growing 
close  together  were  covered  with  fruit.  This  fact  agrees 
better  with  the  belief  that  the  species  is  dioecious  than  that 
it  consists  of  hermaphrodites  and  females;  for  if  any  one 
of  the  isolated  plants  had  been  an  hermaphrodite,  it  would 
probably  have  produced  some  fruit. 


This  great  natural  family  contains  a  much  larger 
number  of  heterostyled  genera  than  any  other  one  as 
yet  known. 

Mitchella  repens.  —  Professor  Asa  Gray  sent  me  sev- 
eral living  plants  collected  when  out  of  flower,  and  near- 
ly half  of  these  proved  long-styled,  and  the  other  half 
short-styled.  The  white  flowers,  which  are  fragrant 
and  which  secrete  plenty  of  nectar,  always  grow  in 
pairs  with  their  ovaries  united,  so  that  the  two  together 
produce  "  a  berry-like  double  drupe."  *  In  my  first 


*  A.  Gray,  '  Manual  of  the  Bot.  of  the  N.  United  States,'  1856,  p.  172. 


126     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

series  of  experiments  (1864)  I  did  not  suppose  that  this 
curious  arrangement  of  the  flowers  would  have  any 
influence  on  their  fertility;  and  in  several  instances 
only  one  of  the  two  flowers  in  a  pair  was  fertilised; 
and  a  large  proportion  or  all  of  these  failed  to  produce 
berries.  In  the  ensuing  year  both  flowers  of  each 
pair  were  invariably  fertilised  in  the  same  manner; 
and  the  latter  experiments  alone  serve  to  show  the 
proportion  of  flowers  which  yield  berries,  when  legiti- 
mately and  illegitimately  fertilised;  but  for  calculating 
the  average  number  of  seeds  per  berry  I  have  used  those 
produced  during  both  seasons. 

In  the  long-styled  flowers  the  stigma  projects  just 
above  the  bearded  throat  of  the  corolla,  and  the 
anthers  are  seated  some  way  down  the  tube.  In  the 
short-styled  flowers  these  organs  occupy  reversed  posi- 
tions. In  this  latter  form  the  fresh  pollen-grains  are 
a  little  larger  and  more  opaque  than  those  of  the  long- 
styled  form.  The  results  of  my  experiments  are  given 
in  Table  21. 

It  follows  from  this  table  that  88  per  cent,  of  the 
paired  flowers  of  both  forms,  when  legitimately  fer- 
tilised, yielded  double  berries,  nineteen  of  which  con- 
tained on  an  average  4.4  seeds,  with  a  maximum  in 
one  of  8  seeds.  Of  the  illegitimately  fertilised  paired 
flowers  only  18  per  cent,  yielded  berries,  six  of  which 
contained  on  an  average  only  2.1  seeds,  with  a  maxi- 
mum in  one  of  4  seeds.  Thus  the  two  legitimate 
unions  are  more  fertile  than  the  two  illegitimate,  ac- 
cording to  the  proportion  of  flowers  which  yielded  ber- 
ries, in  the  ratio  of  100  to  20;  and  according  to  the 
average  number  of  contained  seeds  as  100  to  47. 

Three  long-styled  and  three  short-styled  plants  were 
protected  under  separate  nets,  and  they  produced  alto- 
gether only  8  berries,  containing  on  an  average  only 


CHAP.  III. 


BORRERIA. 


12T 


1.5  seed.  Some  additional  berries  were  produced 
which  contained  no  seeds.  The  plants  thus  treated  were 
therefore  excessively  sterile,  and  their  slight  degree  of 
fertility  may  be  attributed  in  part  to  the  action  of  the 

TABLE  21. 
Mitchella  repens. 


Nature  of  Union. 

Number  of 
Pairs  of 
Flowers  fer- 
tilised   dur- 
ing the  sec- 
ond Season. 

Number 

2STC 

ing  the  sec- 
ond Season. 

Average 
Number  of 
good  Seeds 
per  Drupe 
in  all  the 
Drupes  dur- 

i.±r 

Long-styled  flowers,  by  pollen  of  short-  ! 
styled.    Legitimate  union     j 

9 

8 

4.6 

Long-styled  flowers,  by  own-form  pollen.  I 
Illegitimate  union     j 

8 

3 

2.2 

Short-styled  flowers,  by  pollen  of  long-  1 
styled.    Legitimate  union     j 

8 

7 

4.1 

Short-styled  flowers,  by  own-form  pollen.  ) 
Illegitimate  union    j 

9 

0 

2.0 

The  two  legitimate  unions  together    .    .    . 

17 

15      ' 

4.4 

The  two  illegitimate  unions  together  .    .    . 

17 

3 

2.1 

many  individuals  of  Thrips  which  haunted  the  flowers. 
Mr.  J.  Scott  informs  me  that  a  single  plant  (probably 
a  long-styled  one),  growing  in  the  Botanic  Gardens  at 
Edinburgh,  which  no  doubt  was  freely  visited  by  in- 
sects, produced  plenty  of  berries,  but  how  many  of 
them  contained  seeds  was  not  observed. 

BORRERIA,  NOV.  SP.  NEAR  VALERIANOIDES  (KUBIACE^;). 

Fritz  Miiller  sent  me  seeds  of  this  plant,  which  is 
extremely  abundant  in  St.  Catharina,  in  South  Brazil; 
and  ten  plants  were  raised,  consisting  of  five  long- 
styled  and  five  short-styled.  The  pistil  of  the  long- 
styled  flowers  projects  just  beyond  the  mouth  of  the 
corolla,  and  is  thrice  as  long  as  that  of  the  short- 


128     HETEROSTYLED  DIMORPHIC  PLANTS.     CHAP.  III. 

styled,  and  the  divergent  stigmas  are  likewise  rather 
larger.  The  anthers  in  the  long-styled  form  stand 
low  down  within  the  corolla,  and  are  quite  hidden. 
In  the  short-styled  flowers  the  anthers  project  just 
above  the  mouth  of  the  corolla,  and  the  stigma  stands 
low  down  within  the  tube.  Considering  the  great 
difference  in  the  length  of  the  pistils  in  the  two  forms, 
it  is  remarkable  that  the  pollen-grains  differ  very  little 
in  size,  and  Fritz  Miiller  was  struck  with  the  same 
fact.  In  a  dry  state  the  grains  from  the  short-styled 
flowers  could  just  be  perceived  to  be  larger  than  those 
from  the  long-styled,  and  when  both  were  swollen  by 
immersion  in  water,  the  former  were  to  the  latter  in 
diameter  in  the  ratio  of  100  to  92.  In  the  long-styled 
flowers  beaded  hairs  almost  fill  up  the  mouth  of  the 
corolla  and  project  above  it;  they  therefore  stand 
above  the  anthers  and  beneath  the  stigma.  In  the 
short-styled  flowers  a  similar  brush  of  hairs  is  situated 
low  down  within  the  tubular  corolla,  above  the  stigma 
and  beneath  the  anthers.  The  presence  of  these  beaded 
hairs  in  both  forms,  though  occupying  such  different 
positions,  shows  that  they  are  probably  of  considerable 
functional  importance.  They  would  serve  to  guard 
the  stigma  of  each  form  from  its  own  pollen;  but  in 
accordance  with  Professor  Kerner's  view  *  their  chief 
use  probably  is  to  prevent  the  copious  nectar  being 
stolen  by  small  crawling  insects,  which  could  not  render 
any  services  to  the  species  by  carrying  pollen  from  one 
form  to  the  other. 

The  flowers  are  so  small  and  so  crowded  together 
that  I  was  not  willing  to  expend  time  in  fertilising 
them  separately;  but  I  dragged  repeatedly  heads  of 
short-styled  flowers  over  three  long-styled  flower-heads, 


*  '  Die  Schutzmittel  der  Bliithen  gegen  unberufene  Gaste,'  1876, 


CHAP.  III.  FARAMEA.  129 

0 

which  were  thus  legitimately  fertilised;  and  they  pro- 
duced many  dozen  fruits,  each  containing  two  good 
seeds.  I  fertilised  in  the  same  manner  three  heads 
on  the  same  long-styled  plant  with  pollen  from  another 
long-styled  plant,  so  that  these  were  fertilised  illegiti- 
mately, and  they  did  not  yield  a  single  seed.  Nor  did 
this  plant,  which  was  of  course  protected  by  a  net, 
bear  spontaneously  any  seeds.  Nevertheless  another 
long-styled  plant,  which  was  carefully  protected,  pro- 
duced spontaneously  a  very  few  seeds ;  so  that  the  long- 
styled  form  is  not  always  quite  sterile  with  its  own 
pollen. 

FARAMEA  [SP.  ?]  (KUBIACE^E). 

Fritz  Miiller  has  fully  described  the  two  forms  of 
this  remarkable  plant,  an  inhabitant  of  South  Brazil.* 
In  the  long-styled  form  the  pistil  projects  above  the 
corolla,  and  is  almost  exactly  twice  as  long  as  that  of 
the  short-styled,  which  is  included  within  the  tube. 
The  former  is  divided  into  two  rather  short  and  broad 
stigmas,  whilst  the  short-styled  pistil  is  divided  into 
two  long,  thin,  sometimes  much-curled  stigmas.  The 
stamens  of  each  form  correspond  in  height  or  length 
with  the  pistils  of  the  other  form.  The  anthers  of 
the  short-styled  form  are  a  little  larger  than  those 
of  the  long-styled;  and  their  pollen-grains  are  to 
those  of  the  other  form  as  100  to  67  in  diameter. 
But  the  pollen-grains  of  the  two  forms  differ  in  a 
much  more  remarkable  manner,  of  which  no  other 
instance  is  known;  those  from  the  short-styled  flowers 
being  covered  with  sharp  points;  the  smaller  ones 
from  the  long-styled  being  quite  smooth.  Fritz  Miiller 
remarks  that  this  difference  between  the  pollen-grains 
of  the  two  forms  is  evidently  of  service  to  the  plant; 


*  'Bot.  Zeitung,'  Sept.  10,  1869,  p.  606. 


130     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

for  the  grains  from  the  projecting  stamens  of  the  short- 
styled  form,  if  smooth,  would  have  been  liable  to  be 
blown  away  by  the  wind,  and  would  thus  have  been 
lost;  but  the  little  points  on  their  surfaces  cause  them 
to  cohere,  and  at  the  same  time  favour  their  adhesion 
to  the  hairy  bodies  of  insects,  which  merely  brush 
against  the  anthers  of  these  stamens  whilst  visiting 


Fig.  9. 


Short-styled  f 


Long-Btyled  form. 


Outlines  of  flowers  from  dried  specimens.      Pollen-grains,  magnified 
180  times,  by  Fritz  Miiller. 

FABAMEA  [sp.  ?]. 

the  flowers.  On  the  other  hand,  the  smooth  grains 
of  the  long-styled  flowers  are  safely  included  within 
the  tube  of  the  corolla,  so  that  they  cannot  be  blown 
away,  but  are  almost  sure  to  adhere  to  the  proboscis  of 
an  entering  insect,  which  is  necessarily  pressed  close 
against  the  enclosed  anthers. 

It  may  be  remembered  that  in  the  long-styled  form 


CHAP.  III.  FARAMEA.  131 

of  Linum  perenne  each  separate  stigma  rotates  on  its 
own  axis,  when  the  flower  is  mature,  so  as  to  turn  its 
papillose  surface  outwards.  There  can  be  no  doubt 
that  this  movement,  which  is  confined  to  the  long- 
styled  form,  is  effected  in  order  that  the  proper  sur- 
face of  the  stigma  should  receive  pollen  brought  by 
insects  from  the  other  form.  Now  with  Faramea,  as 
Fritz  Miiller  shows,  it  is  the  stamens  which  rotate  on 
their  axes  in  one  of  the  two  forms,  namely,  the  short- 
styled,  in  order  that  their  pollen  should  be  brushed  off 
by  insects  and  transported  to  the  stigmas  of  the  other 
form.  In  the  long-styled  flowers  the  anthers  of  the 
short  enclosed  stamens  do  not  rotate  on  their  axes, 
but  dehisce  on  their  inner  sides,  as  is  the  common 
rule  with  the  Kubiacea?;  and  this  is  the  best  position 
for  the  adherence  of  the  pollen-grains  to  the  proboscis 
of  an  entering  insect.  Fritz  Miiller  therefore  infers 
that  as  the  plant  became  heterostyled,  and  as  the 
stamens  of  the  short-styled  form  increased  in  length, 
they  gradually  acquired  the  highly  beneficial  power  of 
rotating  on  their  own  axes.  But  he  has  further  shown, 
by  the  careful  examination  of  many  flowers,  that  this 
power  has  not  as  yet  been  perfected ;  and,  consequently, 
that  a  certain  proportion  of  the  pollen  is  rendered  use- 
less, namely,  that  from  the  anthers  which  do  not  rotate 
properly.  It  thus  appears  that  the  development  of  the 
plant  has  not  as  yet  been  completed;  the  stamens  have 
indeed  acquired  their  proper  length,  but  not  their  full 
and  perfect  power  of  rotation.* 


e  Fritz  Muller  gives  another  in-  with  the  nocturnal  habits  of  these 

stance  of  the  want  of  absolute  per-  insects,  most  of  the  flowers  open 

faction  in  the  flowers  of  another  only  during  the  night;  but  some 

member  of  the  Kubiacese,  namely,  open  in  the  day,  and  the  pollen 

Posoqueria     frafirans,    which      is  of  such  flowers  is  robbed,  as  Fritz 

adapted  in  a  most  wonderful  man-  Muller  has  often  seen,  by  humble- 

ner  for  cross-fertilisation  by  the  bees  and   other   insects,   without 

agency  of  moths.     (See  'Bot.  Zeit-  any  benefit  being  thus  conferred 

ung,' 1866,  No.  17.)    In  accordance  on  the  plant. 


132     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

The  several  points  of  difference  in  structure  between 
the  two  forms  of  Faramea  are  highly  remarkable. 
Until  within  the  recent  period,  if  any  one  had  been 
shown  two  plants  which  differed  in  a  uniform  manner 
in  the  length  of  their  stamens  and  pistils, — in  the 
form  of  their  stigmas, — in  the  manner  of  dehiscence 
and  slightly  in  the  size  of  their  anthers, — and  to  an 
extraordinary  degree  in  the  diameter  and  structure  of 
their  pollen-grains,  he  would  have  declared  it  impos- 
sible that  the  two  could  have  belonged  to  one  and  the 
same  species. 

SUTERIA  (species  unnamed  in  the  herbarium  at  Kew) 
(RUBIACE.E). 

I  owe  to  the  kindness  of  Fritz  Miiller  dried  flowers  of 
this  plant  from  St.  Catharina,  in  Brazil.  In  the  long-styled 
form  the  stigma  stands  in  the  mouth  of  the  corolla,  above 
the  anthers,  which  latter  are  enclosed  within  the  tube,  but 
only  a  short  way  down.  In  the  short-styled  form  the  an- 
thers are  placed  in  the  mouth  of  the  corolla  above  the 
stigma,  which  occupies  the  same  position  as  the  anthers  in 
the  other  form,  being  seated  only  a  short  way  down  the 
tube.  Therefore  the  pistil  of  the  long-styled  form  does  not 
exceed  in  length  that  of  the  short-styled  in  nearly  so  great 
a  degree  as  in  many  other  Rubiaceae.  Nevertheless  there 
is  a  considerable  difference  in  the  size  of  the  pollen-grains 
in  the  two  forms;  for,  as  Fritz  Miiller  informs  me,  those 
of  the  short-styled  are  to  those  of  the  long-styled  as  100 
to  75  in  diameter. 

HOUSTONIA   COZRULEA    (RUBIACE^E). 

Professor  Asa  Gray  has  been  so  kind  as  to  send  me  an 
abstract  of  some  observations  made  by  Dr.  Rothrock  on 
this  plant.  The  pistil  is  exserted  in  the  one  form  and  the 
stamens  in  the  other,  as  has  long  been  observed.  The  stig- 
mas of  the  long-styled  form  are  shorter,  stouter,  and  far 
more  hispid  than  in  the  other  form.  The  stigmatic  hairs 
or  papillae  on  the  former  are  .04  mm.,  and  on  the  latter 
only  .023  mm.  in  length.  In  the  short-styled  form  the  an- 


CHAP.  III.  BUBIACILE.  133 

thers  are  larger,  and  the  pollen-grains,  when  distended 
with  water,  are  to  those  from  the  long-styled  form  as  100 
to  72  in  diameter. 

Selected  capsules  from  some  long-styled  plants  growing 
in  the  Botanic  Gardens  at  Cambridge,  U.  S.,  near  where 
plants  of  the  other  form  grew,  contained  on  an  average 
13  seeds;  but  these  plants  must  have  been  subjected  to  un- 
favourable conditions,  for  some  long-styled  plants  in  a 
state  of  nature  yielded  an  average  of  21.5  seeds  per  cap- 
sule. Some  short-styled  plants,  which  had  been  planted  by 
themselves  in  the  Botanic  Gardens,  where  it  was  not  likely 
that  they  would  have  been  visited  by  insects  that  had  pre- 
viously visited  long-styled  plants,  produced  capsules,  eleven 
of  which  were  wholly  sterile,  but  one  contained  4,  and  an- 
other 8  seeds.  So  that  the  short-styled  form  seems  to  be 
very  sterile  with,  its  own  pollen.  Professor  Asa  Gray  in- 
forms me  that  the  other  North  American  species  of  this 
genus  are  likewise  heterostyled. 

OLDEXLANDIA  [SP.?]   (KUBIACE.E). 

Mr.  J.  Scott  sent  me  from  India  dried  flowers  of  a 
heterostyled  species  of  this  genus,  which  is  closely  allied  to 
the  last.  The  pistil  in  the  long-styled  flowers  is  longer  by 
about  a  quarter  of  its  length,  and  the  stamens  shorter  in 
about  the  some  proportion,  than  the  corresponding  organs 
in  the  short-styled  flowers.  In  the  latter  the  anthers  are 
longer,  and  the  divergent  stigmas  decidedly  longer  and 
apparently  thinner  than  in  the  long-styled  form.  Owing 
to  the  state  of  the  specimens,  I  could  not  decide  whether 
the  stigmatic  papillae  were  longer  in  the  one  form  than  in 
the  other.  The  pollen-grains,  distended  with  water,  from 
the  short-styled  flowers  were  to  those  from  the  long-styled 
as  100  to  78  in  diameter,  as  deduced  from  the  mean  of 
ten  measurements  of  each  kind. 

HEDYOTIS  [SP.?]   (RUBIACE.E). 

Fritz  Miiller  sent  me  from  St.  Catharina,  in  Brazil, 
dried  flowers  of  a  small  delicate  species,  which  grows  on 
wet  sand  near  the  edges  of  fresh-water  pools.  In  the  long- 
styled  form  the  stigma  projects  above  the  corolla,  and 
stands  on  a  level  with  the  projecting  anthers  of  the  short- 


134     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

styled  form ;  but  in  the  latter  the  stigmas  stand  rather  be- 
neath the  level  of  the  anthers  in  the  other  or  long-styled 
form,  these  being  enclosed  within  the  tube  of  the  corolla. 
The  pistil  of  the  long-styled  form  is  nearly  thrice  as  long 
as  that  of  the  short-styled,  or,  speaking  strictly,  as"  100  to 
39 ;  and  the  papillae  on  the  stigma  of  the  former  are  broader, 
in  the  ratio  of  4  to  3,  but  whether  longer  than  those  of 
the  short-styled,  I  could  not  decide.  In  the  short-styled 
form  the  anthers  are  rather  larger,  and  the  pollen-grains 
are  to  those  from  the  long-styled  flowers  as  100  to  88  in 
diameter.  Fritz  Miiller  sent  me  a  second,  small-sized  spe- 
cies, which  is  likewise  heterostyled. 

COCCOCYPSELUM    [SP.?]     (KUBIACE.E). 

Fritz  Miiller  also  sent  me  dried  flowers  of  this  plant 
from  St.  Catharina,  in  Brazil.  The  exserted  stigma  of  the 
long-styled  form  stands  a  little  above  the  level  of  the  ex- 
serted anthers  of  the  short-styled  form;  and  the  enclosed 
stigma  of  the  latter  also  stand  a  little  above  the  level  of  the 
enclosed  anthers  in  the  long-styled  form.  The  pistil  of  the 
long-styled  is  about  twice  as  long  as  that  of  the  short- 
styled,  with  its  two  stigmas  considerably  longer,  more  di- 
vergent, and  more  curled.  Fritz  Miiller  informs  me  that 
he  could  detect  no  difference  in  the  size  of  the  pollen- 
grains  in  the  two  forms.  Nevertheless,  there  can  be  no 
doubt  that  this  plant  is  heterostyled. 

LIPOSTOMA  [SP.?]  (BUBIACE.E). 

Dried  flowers  of  this  plant,  which  grows  in  small  wet 
ditches  in  St.  Catharina,  in  Brazil,  were  likewise  sent  me 
by  Fritz  Miiller.  In  the  long-styled  form  the  exserted 
stigma  stands  rather  above  the  level  of  the  exserted  anthers 
of  the  other  form ;  whilst  in  the  short-styled  form  it  stands 
on  a  level  with  the  anthers  of  the  other  form.  So  that  the 
want  of  strict  correspondence  in  height  between  the  stig- 
mas and  anthers  in  the  two  forms  is  reversed,  compared 
with  what  occurs  in  Hedyotis.  The  long-styled  pistil  is  to 
that  of  the  short-styled  as  100  to  36  in  length;  and  its 
divergent  stigmas  are  longer  by  fully  one-third  of  their 
own  length  than  those  of  the  short-styled  form.  In  the 
latter  the  anthers  are  a  little  larger,  and  the  pollen-grains 


CHAP.  III.  RUBIACE^E.  135 

are  as  100  to  80  in  diameter,  compared  with  those  from  the 
long-styled  form. 

CINCHONA  MICRANTHA  (EUSTACES). 

Dried  specimens  of  both  forms  of  this  plant  were  sent 
me  from  Kew.*  In  the  long-styled  form  the  apex  of  the 
stigma  stands  just  beneath  the  bases  of  the  hairy  lobes  of 
the  corolla;  whilst  the  summits  of  the  anthers  are  seated 
about  halfway  down  the  tube.  The  pistil  is  in  length  as 
100  to  38  to  that  of  the  short-styled  form.  In  the  latter 
the  anthers  occupy  the  same  position  as  the  stigma  of  the 
other  form,  and  they  are  considerably  longer  than  those  of 
the  long-styled  form.  As  the  summit  of  the  stigma  in  the 
short-styled  form  stands  beneath  the  bases  of  the  anthers, 
which  are  seated  halfway  down  the  corolla,  the  style  has 
been  extremely  shortened  in  this  form;  its  length  to  that 
of  the  long-styled  being,  in  the  specimens  examined,  only 
as  5.3  to  100 !  The  stigma,  also,  in  the  short-styled  form  is 
very  much  shorter  than  that  in  the  long-styled,  in  the  ratio 
of  57  to  100.  The  pollen-grains  from  the  short-styled 
flowers,  after  having  been  soaked  in  water,  were  rather 
larger — in  about  the  ratio  of  100  to  91 — than  those  from 
the  long-styled  flowers,  and  they  were  more  triangular, 
with  the  angles  more  prominent.  As  all  the  grains  from 
the  short-styled  flowers  were  thus  characterised,  and  as 
they  had  been  left  in  water  for  three  days,  I  am  convinced 
that  this  difference  in  shape  in  the  two  sets  of  grains  can- 
not be  accounted  for  by  unequal  distension  with  water. 

Besides  the  several  Rubiaceous  genera  already  men- 
tioned, Fritz  Miiller  informs  me  that  two  or  three  species 
of  Psychotria  and  Rudgea  eriantha,  natives  of  St.  Catha- 
rina,  in  Brazil,  are  heterostyled,  as  is  Manettia  bicolor.  I 
may  add  that  I  formerly  fertilised  with  their  own  pollen 
several  flowers  on  a  plant  of  this  latter  species  in  my  hot- 
house, but  they  did  not  set  a  single  fruit.  From  Wight 
and  Arnott's  description,  there  seems  to  be  little  doubt  that 
Knoxia  in  India  is  heterostyled;  and  Asa  Gray  is  con- 
vinced that  this  is  the  case  with  Diodia  and  Spermacoce 


*  My  attention  was  called  to  this    given    by  Mr.   Markham    in  his 
plant  by  a  drawing  copied  from    'Travels  in  Peru,' p.  539. 
Howard's    'Quinologia,'    Tab.    3, 


136     HETEROSTYLED  DIMORPHIC  PLANTS.    CHAP.  III. 

in  the  United  States.  Lastly,  from  Mr.  W.  W.  Bailey's 
description,*  it  appears  that  the  Mexican  Bouvardia  le- 
iantha  is  heterostyled. 

Altogether  we  now  know  of  17  heterostyled  genera 
in  the  great  family  of  the  Bubiaceae;  though  more 
information  is  necessary  with  respect  to  some  of  them, 
more  especially  those  mentioned  in  the  last  para- 
graph, before  we  can  feel  absolutely  safe.  In  the 
*  Genera  Plantarum/  by  Bentham  and  Hooker,  the 
Bubiaceae  are  divided  into  25  tribes,  containing  337 
genera;  and  it  deserves  notice  that  the  genera  now 
known  to  be  heterostyled  are  not  grouped  in  one  or 
two  of  these  tribes,  but  are  distributed  in  no  less  than 
eight  of  them.  From  this  fact  we  may  infer  that 
most  of  the  genera  have  acquired  their  heterostyled 
structure  independently  of  one  another;  that  is,  they 
have  not  inherited  this  structure  from  some  one  or 
even  two  or  three  progenitors  in  common.  It  further 
deserves  notice  that  in  the  homostyled  genera,  as  I 
am  informed  by  Professor  Asa  Gray,  the  stamens  are 
either  exserted  or  are  included  within  the  tube  of  the 
corolla,  in  a  nearly  constant  manner;  so  that  this  char- 
acter, which  is  not  even  of  specific  value  in  the  hetero- 
styled species,  is  often  of  generic  value  in  other  mem- 
bers of  the  family. 


*  'Bull,  of  the  Torrey  Bot.  Club,'  1876,  p.  106. 


CHAP.  IV.  LYTHRUM  SALICARIA.  137 


CHAPTER  IV. 

HETEEOSTYLED  TEIMOEPHIC  PLANTS. 

Lythrum  salicaria — Description  of  the  three  forms — Their  power  and 
complex  manner  of  fertilising  one  another — Eighteen  different 
unions  possible — Mid-styled  form  eminently  feminine  in  nature — 
Lythrum  Grsefferi  likewise  trimorphic — L.  thymifolia  dimorphic — 
L.  hyssopifolia  homostyled — Nessea  verticillata  trimorphic— Lager- 
strosmia,  nature  doubtful — Oxalis,  trimorphic  species  of— O.  Valdi- 
viana — O.  Regnelli,  the  illegitimate  unions  quite  barren — O.  spe- 
ciosa — 0.  sensitiva — Homostyled  species  of  Oxalis— Pontederia, 
the  one  monocotyledonous  genus  known  to  include  heterostyled 
species. 

IN"  the  previous  chapters  various  heterostyled  dimor- 
phic plants  have  been  described,  and  now  we  come  to 
heterostyled  trimorphic  plants,  or  those  which  present 
three  forms.  These  have  been  observed  in  three 
families,  and  consist  of  species  of  Lythrum  and  of  the 
allied  genus  Nesaea,  of  Oxalis  and  Pontederia.  In 
their  manner  of  fertilisation  these  plants  offer  a  more 
remarkable  case  than  can  be  found  in  any  other  plant 
or  animal. 

Lythrum  salicaria. — The  pistil  in  each  form  differs 
from  that  in  either  of  the  other  forms,  and  in  each 
there  are  two  sets  of  stamens  different  in  appearance 
and  function.  But  one  set  of  stamens  in  each  form 
corresponds  with  a  set  in  one  of  the  other  two  forms. 
Altogether  this  one  species  includes  three  females  or 
female  organs  and  three  sets  of  male  organs,  all  as 
distinct  from  one  another  as  if  they  belonged  to  dif- 
ferent species;  and  if  smaller  functional  differences 


138    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

are  considered,  there  are  five  distinct  sets  of  males. 
Two  of  the  three  hermaphrodites  must  coexist,  and 
pollen  must  be  carried  by  insects  reciprocally  from  one 
to  the  other,  in  order  that  either  of  the  two  should  be 
fully  fertile;  but  unless  all  three  forms  coexist,  two 
sets  of  stamens  will  be  wasted,  and  the  organisation  of 
the  species,  as  a  whole,  will  be  incomplete.  On  the 
other  hand,  when  all  three  hermaphrodites  coexist,  and 
pollen  is  carried  from  one  to  the  other,  the  scheme 
is  perfect;  there  is  no  waste  of  pollen  and  no  false 
co-adaptation.  In  short,  nature  has  ordained  a  most 
complex  marriage-arrangement,  namely,  a  triple  union 
between  three  hermaphrodites, — each  hermaphrodite 
being  in  its  female  organ  quite  distinct  from  the 
other  two  hermaphrodites  and  partially  distinct  in 
its  male  organs,  and  each  furnished  with  two  sets  of 
males. 

The  three  forms  may  be  conveniently  called,  from 
the  unequal  lengths  of  their  pistils,  the  long-styled,  mid- 
styled,  and  short-styled.  The  stamens  also  are  of  un- 
equal length,  and  these  may  be  called  the  longest,  mid- 
length,  and  shortest.  Two  sets  of  stamens  of  different 
length  are  found  in  each  form.  The  existence  of  the 
three  forms  was  first  observed  by  Vaucher,*  and  subse- 
quently more  carefully  by  Wirtgen ;  but  these  botanists, 
not  being  guided  by  any  theory  or  even  suspicion  of 
their  functional  differences,  did  not  perceive  some  of  the 
most  curious  points  of  difference  in  their  structure.  I 
will  first  briefly  describe  the  three  forms  by  the  aid  of 
the  accompanying  diagram,  which  shows  the  flowers, 
six  times  magnified,  in  their  natural  position,  with  their 
petals  and  calyx  on  the  near  side  removed. 


*  'Hist.  Phys.  des  Plantes  und  dessen  Formen,"  'Verhand. 
d'Europe,'  torn,  ii.,  1841,  p.  371.  des  naturlmt.  Vereins  fur  preuss. 
Wirtgen,  "UeberLy/Arwmsah'caria  Rheinl.,'  5.  Jahrgang,  1848,  S.  7. 


CHAP.  IV.  LYTHRUM  SALICAEIA. 

Fig.  10. 


139 


Micl- 
Btyled 


Short- 
styled. 


Diagram  of  the  flowers  of  the  three  forms  of  Lythrum  salicaria,  in 
their  natural  position,  with  the  petals  and  calyx  removed  on  the  near 
side :  enlarged  six  times. 

The  dotted  lines  with  the  arrows  show  the  directions  in  which 
pollen  must  be  carried  to  each  stigma  to  ensure  full  fertility. 


140    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

Long-styled  form. — This  form  can  be  at  once  recog- 
nised by  the  length  of  the  pistil,  which  is  (including 
the  ovarium)  fully  one-third  longer  than  that  of  the 
mid-styled  and  more  than  thrice  as  long  as  that  of  the 
short-styled  form.  It  is  so  disproportionately  long, 
that  it  projects  in  the  bud  through  the  folded  petals. 
It  stands  out  considerably  beyond  the  mid-length  sta- 
mens; its  terminal  portion  depends  a  little,  but  the 
stigma  itself  is  slightly  upturned.  The  globular  stigma 
is  considerably  larger  than  that  of  the  other  two  forms, 
with  the  papillae  on  its  surface  generally  longer.  The 
six  mid-length  stamens  project  about  two-thirds  the 
length  of  the  pistil,  and  correspond  in  length  with  the 
pistil  of  the  mid-styled  form.  Such  correspondence 
in  this  and  the  two  following  forms  is  generally  very 
close;  the  difference,  where  there  is  any,  being  usually 
in  a  slight  excess  of  length  in  the  stamens.  The  six 
shortest  stamens  lie  concealed  within  the  calyx;  their 
ends  are  turned  up  and  they  are  graduated  in  length, 
so  as  to  form  a  double  row.  The  anthers  of  these  sta- 
mens are  smaller  than  those  of  the  mid-length  ones. 
The  pollen  is  of  the  same  yellow  colour  in  both  sets. 
H.  Miiller*  measured  the  pollen-grain  in  all  three 
forms,  and  his  measurements  are  evidently  more  trust- 
worthy than  those  which  I  formerly  made,  so  I  will 
give  them.  The  numbers  refer  to  divisions  of  the 
micrometer  equalling  g-^  mm.  The  grains,  distended 
with  water,  from  the  mid-length  stamens  are  7-7f, 
and  those  from  the  shortest  stamens  6-6^  in  diameter, 
or  as  100  to  86.  The  capsules  of  this  form  contain 
on  an  average  93  seeds;  how  this  average  was  ob- 
tained will  be  presently  explained.  As  these  seeds, 
when  cleaned,  seemed  larger  than  those  from  the  mid- 


*  '  Die  Befruchtung  der  Blumen,'  1873,  p.  193. 


CHAP.  IV.  LYTERUM  SALICARIA.  141 

styled  or  short-styled  forms,  100  of  them  were  placed 
in  a  good  balance,  and  by  the  double  method  of  weigh- 
ing were  found  to  equal  121  seeds  of  the  mid-styled  or 
142  of  the  short-styled;  so  that  five  long-styled  seeds 
very  nearly  equal  six  mid-styled  or  seven  short-styled 
seeds. 

Mid-styled  form. — The  pistil  occupies  the  position 
represented  in  the  diagram,  with  its  extremity  con- 
siderably upturned,  but  to  a  variable  degree;  the 
stigma  is  seated  between  the  anthers  of  the  longest 
and  the  shortest  stamens.  The  six  longest  stamens 
correspond  in  length  with  the  pistil  of  the  long-styled 
form;  their  filaments  are  coloured  bright  pink;  the 
anthers  are  dark-coloured,  but  from  containing  bright- 
green  pollen  and  from  their  early  dehiscence  they  appear 
emerald-green.  Hence  in  general  appearance  these 
stamens  are  remarkably  dissimilar  from  the  mid-length 
stamens  of  the  long-styled  form.  The  six  shortest  sta- 
mens are  enclosed  within  the  calyx,  and  resemble  in 
all  respects  the  shortest  stamens  of  the  long-styled 
form;  both  these  sets  correspond  in  length  with  the 
short  pistil  of  the  short-styled  form.  The  green  pol- 
len-grains of  the  longest  stamens  are  9-10  in  di- 
ameter, whilst  the  yellow  grains  from  the  shortest 
stamens  are  only  6;  or  as  100  to  63.  But  the  pollen- 
grains  from  different  plants  appeared  to  me,  in  this 
case  and  others,  to  be  in  some  degree  variable  in  size. 
The  capsules  contain  on  an  average  130  seeds;  but  per- 
haps, as  we  shall  see,  this  is  rather  too  high  an  aver- 
age. The  seeds  themselves,  as  before  remarked,  are 
smaller  than  those  of  the  long-styled  form. 

Short-styled  form. — The  pistil  is  here  very  short,  not 
one-third  of  the  length  of  that  of  the  long-styled  form. 
It  is  enclosed  within  the  calyx,  which,  differently  from 
that  in  the  other  two  forms,  does  not  enclose  any  an- 


142    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

thers.  The  end  of  the  pistil  is  generally  bent  upwards 
at  right  angles.  The  six  longest  stamens,  with  their 
pink  filaments  and  green  pollen,  resemble  the  corre- 
sponding stamens  of  the  mid-styled  form.  But  accord- 
ing to  H.  Miiller,  their  pollen-grains  are  a  little  larger, 
viz.  9^-1 0|,  instead  of  9-10  in  diameter.  The  six 
mid-length  stamens,  with  their  uncoloured  filaments 
and  yellow  pollen,  resemble  in  the  size  of  their  pollen- 
grains  and  in  all  other  respects  the  corresponding 
stamens  of  the  long-styled  form.  The  difference  in 
diameter  between  the  grains  from  the  two  sets  of 
anthers  in  the  short-styled  form  is  as  100  to  73. 
The  capsules  contain  fewer  seeds  on  an  average  than 
those  of  either  of  the  preceding  forms,  namely,  83.5; 
and  the  seeds  are  considerably  smaller.  In  this  latter 
respect,  but  not  in  number,  there  is  a  gradation 
parallel  to  that  in  the  length  of  the  pistil,  the  long- 
styled  having  the  largest  seeds,  the  mid-styled  the 
next  in  size,  and  the  short-styled  the  smallest. 

We  thus  see  that  this  plant  exists  under  three 
female  forms,  which  differ  in  the  length  and  curva- 
ture of  the  style,  in  the  size  and  state  of  the  stigma, 
and  in  the  number  and  size  of  the  seed.  There  are 
altogether  thirty-six  males  or  stamens,  and  these  can 
be  divided  into  three  sets  of  a  dozen  each,  differing 
from  one  another  in  length,  curvature,  and  colour  of 
the  filaments, — in  the  size  of  the  anthers,  and  especially 
in  the  colour  and  diameter  of  the  pollen-grains.  Each 
form  bears  half-a-dozen  of  one  kind  of  stamens  and 
half-a-dozen  of  another  kind,  but  not  all  three  kinds. 
The  three  kinds  of  stamens  correspond  in  length  with 
the  three  pistils:  the  correspondence  is  always  between 
half  of  the  stamens  in  two  of  the  forms  with  the  pistil 
of  the  third  form.  The  following  table  of  the  diameters 
of  the  pollen-grains,  after  immersion  in  water,  from 


CHAP.  IV.  LYTHRUM  SALICARIA.  143 

both  sets  of  stamens  in  all  three  forms,  is  copied  from 
H.  Miiller;    they  are  arranged  in  the  order  of  their 

size : — 

Pollen-grains  from  longest  stamens  of  short-styled  form    9J  to  10J 


mid-styled 

mid-length  stamens  of  long-styled 
short-styled 

shortest  stamens  of  long-styled 
"  "  mid-styled 


We  here  see  that  the  largest  pollen-grains  come  from 
the  longest  stamens  and  the  least  from  the  shortest; 
the  extreme  difference  in  diameter  between  them  being 
as  100  to  60. 

The  average  number  of  seeds  in  the  three  forms  was 
ascertained  by  counting  them  in  eight  fine  selected 
capsules  taken  from  plants  growing  wild,  and  the 
result  was,  as  we  have  seen,  for  the  long-styled  (neg- 
lecting decimals)  93,  mid-styled  130,  and  short-styled 
83.  I  should  not  have  trusted  in  these  ratios  had  I 
not  possessed  a  number  of  plants  in  my  garden  which, 
owing  to  their  youth,  did  not  yield  the  full  comple- 
ment of  seed,  but  were  of  the  same  age  and  grew 
under  the  same  conditions,  and  were  freely  visited  by 
bees.  I  took  six  fine  capsules  from  each,  and  found 
the  average  to  be  for  the  long-styled  80,  for  the  mid- 
styled  97,  and  for  the  short-styled  61.  Lastly,  legiti- 
mate unions  effected  by  me  between  the  three  forms 
gave,  as  may  be  seen  in  the  following  tables,  for  the 
long-styled  an  average  of  90  seeds,  for  the  mid-styled 
117,  and  for  the  short-styled  71.  So  that  we  have 
good  concurrent  evidence  of  a  difference  in  the  average 
production  of  seed  by  the  three  forms.  To  show  that 
the  unions  effected  by  me  often  produced  their  full 
effect  and  may  be  trusted,  I  may  state  that  one  mid- 
styled  capsule  yielded  151  good  seeds,  which  is  the 


HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


same  number  as  in  the  finest  wild  capsule  which  I 
examined.  Some  artificially  fertilised  short  and  long- 
styled  capsules  produced  a  greater  number  of  seeds  than 
was  ever  observed  by  me  in  wild  plants  of  the  same 
forms,  but  then  I  did  not  examine  many  of  the  latter. 
This  plant,  I  may  add,  offers  a  remarkable  instance 
how  profoundly  ignorant  we  are  of  the  life-conditions  of 
a  species.  Naturally  it  grows  "  in  wet  ditches,  watery 
places,  and  especially  on  the  banks  of  streams,"  and 
though  it  produces  so  many  minute  seeds,  it  never 
spreads  on  the  adjoining  land ;  yet,  when  planted  in  my 
garden,  on  clayey  soil  lying  over  chalk,  and  which  is  so 
dry  that  a  rush  cannot  be  found,  it  thrives  luxuriantly, 
grows  to  above  6  feet  in  height,  produces  self-sown 
seedlings,  and  (which  is  a  severer  test)  is  as  fertile  as 
in  a  state  of  nature.  Nevertheless  it  would  be  almost 
a  miracle  to  find  this  plant  growing  spontaneously  on 
such  land  as  that  in  my  garden. 

According  to  Vaucher  and  Wirtgen,  the  three  forms 
coexist  in  all  parts  of  Europe.  Some  friends  gathered 
for  me  in  North  Wales  a  number  of  twigs  from  sepa- 
rate plants  growing  near  one  another,  and  classified 
them.  My  son  did  the  same  in  Hampshire,  and  here 
is  the  result: — 

TABLE  22. 


— 

Long-styled. 

Mid  «tyled. 

Short-styled. 

Total. 

North  Wales  
Hampshire      

95 
53 

97 
38 

72 

38 

264 

129 

Total 

148 

135 

110 

393 

If  twice  or  thrice  the  number  had  been  collected, 
the  three  forms  would  probably  have  been  found 
nearly  equal;  I  infer  this  from  considering  the  above 
figures,  and  from  my  son  telling  me  that  if  he  had 


CHAP.  IV.  LYTHRTJM  SALICARIA.  145 

collected  in  another  spot  he  felt  sure  that  the  mid- 
styled  plants  would  have  been  in  excess.  I  several 
times  sowed  small  parcels  of  seed,  and  raised  all  three 
forms;  but  I  neglected  to  record  the  parent-form,  ex- 
cepting in  one  instance,  in  which  I  raised  from  short- 
styled  seed  twelve  plants,  of  which  only  one  turned  out 
long-styled,  four  mid-styled,  and  seven  short-styled. 

Two  plants  of  each  form  were  protected  from  the 
access  of  insects  during  two  successive  years,  and  in  the 
autumn  they  yielded  very  few  capsules  and  presented 
a  remarkable  contrast  with  the  adjoining  uncovered 
plants,  which  were  densely  covered  with  capsules.  In 
1863  a  protected  long-styled  plant  produced  only  five 
poor  capsules ;  two  mid-styled  plants  produced  together 
the  same  number;  and  two  short-styled  plants  only  a 
single  one.  These  capsules  contained  very  few  seeds; 
yet  the  plants  were  fully  productive  when  artificially 
fertilised  under  the  net.  In  a  state  of  nature  the 
flowers  are  incessantly  visited  for  their  nectar  by  hive- 
and  other  bees,  various  Diptera  and  Lepidoptera.*  The 
nectar  is  secreted  all  round  the  base  of  the  ovarium; 
but  a  passage  is  formed  along  the  upper  and  inner 
side  of  the  flower  by  the  lateral  deflection  (not  repre- 
sented in  the  diagram)  of  the  basal  portions  of  the 
filaments;  so  that  insects  invariably  alight  on  the  pro- 
jecting stamens  and  pistil,  and  insert  their  proboscides 
along  the  upper  and  inner  margin  of  the  corolla.  We 
can  now  see  why  the  ends  of  the  stamens  with  their 
anthers,  and  the  ends  of  the  pistils  with  their  stigmas, 
are  a  little  upturned,  so  that  they  may  be  brushed  by 
the  lower  hairy  surfaces  of  the  insects'  bodies.  The 
shortest  stamens  which  lie  enclosed  within  the  calyx  of 


*  H.  Muller  gives  a  list  of  the  one  bee,  the  Cilissa  melannra,  al- 
species,  'Die  Befruchtung  der  most  confines  its  visits  to  this 
Blumen,'  p.  196.  It  appears  that  plant. 


146    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

the  long-  and  mid-styled  forms  can  be  touched  only  by 
the  proboscis  and  narrow  chin  of  a  bee;  hence  they 
have  their  ends  more  upturned,  and  they  are  graduated 
in  length,  so  as  to  fall  into  a  narrow  file,  sure  to  be 
raked  by  the  thin  intruding  proboscis.  The  anthers  of 
the  longer  stamens  stand  laterally  farther  apart  and  are 
more  nearly  on  the  same  level,  for  they  have  to  brush 
against  the  whole  breadth  of  the  insect's  body.  In 
very  many  other  flowers  the  pistil,  or  the  stamens,  or 
both,  are  rectangularly  bent  to  one  side  of  the  flower. 
This  bending  may  be  permanent,  as  with  Lythrum 
and  many  others,  or  may  be  effected,  as  in  Dictam- 
nus  frqxinella  and  others,  by  a  temporary  movement, 
which  occurs  in  the  case  of  the  stamens,  when  the 
anthers  dehisce,  and  in  the  case  of  the  pistil  when 
the  stigma  is  mature;  but  these  two  movements  do 
not  always  take  place  simultaneously  in  the  same 
flower.  Now  I  have  found  no  exception  to  the  rule, 
that  when  the  stamens  and  pistil  are  bent,  they  bend 
to  that  side  of  the  flower  which  secretes  nectar,  even 
though  there  be  a  rudimentary  nectary  of  large  size 
on  the  opposite  side,  as  in  some  species  of  Corydalis. 
When  nectar  is  secreted  on  all  sides,  they  bend  to 
that  side  where  the  structure  of  the  flower  allows  the 
easiest  access  to  it,  as  in  Lythrum,  various  Papilio- 
nacese,  and  others.  The  rule  consequently  is,  that 
when  the  pistils  and  stamens  are  curved  or  bent,  the 
stigma  and  anthers  are  thus  brought  into  the  path- 
way leading  to  the  nectary.  There  are  a  few  cases 
which  seem  to  be  exceptions  to  this  rule,  but  they  are 
not  so  in  truth;  for  instance,  in  the  Gloriosa  lily,  the 
stigma  of  the  grotesque  and  rectangularly  bent  pistil 
is  brought,  not  into  any  pathway  from  the  outside 
towards  the  nectar-secreting  recesses  of  the  flower,  but 
into  the  circular  route  which  insects  follow  in  proceed- 


CHAP.  IV.  LYTHRUM  SALICARIA.  147 

ing  from  one  nectary  to  the  other.  In  Scrophularia 
aquatica  the  pistil  is  bent  downwards  from  the  mouth 
of  the  corolla,  but  it  thus  strikes  the  pollen-dusted 
breast  of  the  wasps  which  habitually  visit  these  ill- 
scented  flowers.  In  all  these  cases  we  see  the  supreme 
dominating  power  of  insects  on  the  structure  of  flowers, 
especially  of  those  which  have  irregular  corollas. 
Flowers  which  are  fertilised  by  the  wind  must  of  course 
be  excepted;  but  I  do  not  know  of  a  single  instance 
of  an  irregular  flower  which  is  thus  fertilised. 

Another  point  deserves  notice.  In  each  of  the  three 
forms  two  sets  of  stamens  correspond  in  length  with 
the  pistils  in  the  other  two  forms.  When  bees  suck  the 
flowers,  the  anthers  of  the  longest  stamens,  bearing  the 
green  pollen,  are  rubbed  against  the  abdomen  and  the 
inner  sides  of  the  hind  legs,  as  is  likewise  the  stigma  of 
the  long-styled  form.  The  anthers  of  the  mid-length 
stamens  and  the  stigma  of  the  mid-styled  form  are 
rubbed  against  the  under  side  of  the  thorax  and  be- 
tween the  front  pair  of  legs.  And,  lastly,  the  anthers 
of  the  shortest  stamens  and  the  stigma  of  the  short- 
styled  form  are  rubbed  against  the  proboscis  and  chin; 
for  the  bees  in  sucking  the  flowers  insert  only  the  front 
part  of  their  heads  into  the  flower.  On  catching  bees,  I 
observed  much  green  pollen  on  the  inner  sides  of  the 
hind  legs  and  on  the  abdomen,  and  much  yellow 
pollen  on  the  under  side  of  the  thorax.  There  was 
also  pollen  on  the  chin,  and,  it  may  be  presumed,  on 
the  proboscis,  but  this  was  difficult  to  observe.  I  had, 
however,  independent  proof  that  pollen  is  carried  on 
the  proboscis;  for  a  small  branch  of  a  protected  short- 
styled  plant  (which  produced  spontaneously  only  two 
capsules)  was  accidentally  left  during  several  days 
pressing  against  the  net,  and  bees  were  seen  inserting 
their  proboscides  through  the  meshes,  and  in  conse- 


148    HETEEOSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

quence  numerous  capsules  were  formed  on  this  one 
small  branch.  From  these  several  facts  it  follows  that 
insects  will  generally  carry  the  pollen  of  each  form  from 
the  stamens  to  the  pistil  of  corresponding  length;  and 
we  shall  presently  see  the  importance  of  this  adapta- 
tion. It  must  not,  however,  be  supposed  that  the  bees 
do  not  get  more  or  less  dusted  all  over  with  the  several 
kinds  of  pollen;  for  this  could  be  seen  to  occur  with 
the  green  pollen  from  the  longest  stamens.  Moreover 
a  case  will  presently  be  given  of  a  long-styled  plant 
producing  an  abundance  of  capsules,  though  grow- 
ing quite  by  itself,  and  the  flowers  must  have  been 
fertilised  by  their  own  two  kinds  of  pollen;  but 
these  capsules  contained  a  very  poor  average  of  seed. 
Hence  insects,  and  chiefly  bees,  act  both  as  general  car- 
riers of  pollen,  and  as  special  carriers  of  the  right  sort. 
Wirtgen  remarks  *  on  the  variability  of  this  plant  in 
the  branching  of  the  stem,  in  the  length  of  the  bractese, 
size  of  the  petals,  and  in  several  other  characters.  The 
plants  which  grew  in  my  garden  had  their  leaves, 
which  differed  much  in  shape,  arranged  oppositely, 
alternately,  or  in  whorls  of  three.  In  this  latter  case 
the  stems  were  hexagonal;  those  of  the  other  plants 
being  quadrangular.  But  we  are  concerned  chiefly 
with  the  reproductive  organs:  the  upward  bending  of 
the  pistil  is  variable  and  especially  in  the  short-styled 
form,  in  which  it  is  sometimes  straight,  sometimes 
slightly  curved,  but  generally  bent  at  right  angles. 
The  stigma  of  the  long-styled  pistil  frequently  has 
longer  papillae  or  is  rougher  than  that  of  the  mid- 
styled  and  the  latter  than  that  of  the  short-styled; 
but  this  character,  though  fixed  and  uniform  in  the 
two  forms  of  Primula  veris,  &c.,  is  here  variable,  for 


*  'Verhand.  des  naturhist.  Vereins,  fur  Pr.  Bheinl.,'  5.  Jahrgang, 
1848,  pp.  11,  13. 


CHAP.  IV.  LYTHRUM  SALICARIA.  149 

I  have  seen  mid-styled  stigmas  rougher  than  those 
of  the  long-styled.*  The  degree  to  which  the  longest 
and  mid-length  stamens  are  graduated  in  length  and 
have  their  ends  upturned  is  variable;  sometimes  all 
are  equally  long.  The  colour  of  the  green  pollen  in 
the  longest  stamens  is  variable,  being  sometimes  pale 
greenish-yellow;  in  one  short-styled  plant  it  was  almost 
white.  The  grains  vary  a  little  in  size:  I  examined 
one  short-styled  plant  with  the  grains  above  the 
average  size;  and  I  have  seen  a  long-styled  plant  with 
the  grains  from  the  mid-length  and  shortest  anthers  of 
the  same  size.  We  here  see  great  variability  in  many 
important  characters;  and  if  any  of  these  variations 
were  of  service  to  the  plant,  or  were  correlated  with 
useful  functional  differences,  the  species  is  in  that  state 
in  which  natural  selection  might  readily  do  much  for 
its  modification. 

On  the  Power  of  Mutual  Fertilisation  between  the 

three  Forms. 

Nothing  shows  more  clearly  the  extraordinary  com- 
plexity of  the  reproductive  system  of  this  plant  than 
the  necessity  of  making  eighteen  distinct  unions  in 
order  to  ascertain  the  relative  fertilising  power  of  the 
three  forms.  Thus  the  long-styled  form  has  to  be  fer- 
tilised with  pollen  from  its  own  two  kinds  of  anthers, 
from  the  two  in  the  mid-styled,  and  from  the  two  in 
the  short-styled  form.  The  same  process  has  to  be 
repeated  with  the  mid-styled  and  short-styled  forms. 
It  might  have  been  thought  sufficient  to  have  tried  on 
each  stigma  the  green  pollen,  for  instance,  from  either 

*  The  plants  which  I  observed  and  he  appears  to  have  found  the 
grew  in  my  garden,  and  probably  stigmatic  papillae  differing  con- 
varied  rather  more  than  those  stantly  in  length  and  structure  in 
growing  in  a  state  of  nature.  H.  the  three  forms,  being  longest  in 
Miiller  has  described  the  stigmas  the  long-styled  form, 
of  all  three  forms  with  great  care, 


150    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

the  mid-  or  the  short-styled  longest  stamens,  and  not 
from  both;  but  the  result  proves  that  this  would 
have  been  insufficient,  and  that  it  was  necessary  to 
try  all  six  kinds  of  pollen  on  each  stigma.  As  in 
fertilising  flowers  there  will  always  be  some  failures, 
it  would  have  been  advisable  to  have  repeated  each  of 
the  eighteen  unions  a  score  of  times;  but  the  labour 
would  have  been  too  great;  as  it  was,  I  made  223 
unions,  i.  e.  on  an  average  I  fertilised  above  a  dozen 
flowers  in  the  eighteen  different  methods.  Each  flower 
was  castrated,  the  adjoining  buds  had  to  be  removed, 
so  that  the  flowers  might  be  safely  marked  with 
thread,  wool,  &c. ;  and  after  each  fertilisation  the  stig- 
ma was  examined  with  a  lens  to  see  that  there  was  suffi- 
cient pollen  on  it.  Plants  of  all  three  forms  were 
protected  during  two  years  by  large  nets  on  a  frame- 
work; two  plants  were  used  during  one  or  both  years, 
in  order  to  avoid  any  individual  peculiarity  in  a  par- 
ticular plant.  As  soon  as  the  flowers  had  withered, 
the  nets  were  removed;  and  in  the  autumn  the  cap- 
sules were  daily  inspected  and  gathered,  the  ripe 
seeds  being  counted  under  the  microscope.  I  have 
given  these  details  that  confidence  may  be  placed 
in  the  following  tables,  and  as  some  excuse  for  two 
blunders  which  I  believe  were  made.  These  blunders 
are  referred  to,  with  their  probable  cause,  in  two 
foot-notes  to  the  tables.  The  erroneous  numbers,  how- 
ever, are  entered  in  the  tables,  that  it  may  not  be  sup- 
posed that  I  have  in  any  one  instance  tampered  with 
the  results. 

A  few  words  explanatory  of  the  three  tables  must  be 
given.  Each  is  devoted  to  one  of  the  three  forms,  and 
is  divided  into  six  compartments.  The  two  upper  ones 
in  each  table  show  the  number  of  good  seeds  resulting 
from  the  application  to  the  stigma  of  pollen  from  the 


CIIAP.  IV.  LYTHRUM  SALICARIA.  151 

two  sets  of  stamens  which  correspond  in  length  with 
the  pistil  of  that  form,  and  which  are  borne  by  the 
other  two  forms.  Such  unions  are  of  a  legitimate 
nature.  The  two  next  lower  compartments  show  the 
result  of  the  application  of  pollen  from  the  two  sets  of 
stamens  not  corresponding  in  length  with  the  pistil, 
and  which  are  borne  by  the  other  two  forms.  These 
unions  are  illegitimate.  The  two  lowest  compartments 
show  the  result  of  the  application  of  each  form's  own 
two  kinds  of  pollen  from  the  two  sets  of  stamens  be- 
longing to  the  same  form  and  which  do  not  equal  the 
pistil  in  length.  These  unions  are  likewise  illegiti- 
mate. .  The  term  "  own- form  pollen  "  here  used  does 
not  mean  pollen  from  the  flower  to  be  fertilised — for 
this  was  never  used — but  from  another  flower  on  the 
same  plant,  or  more  commonly  from  a  distinct  plant  of 
the  same  form.  The  figure  (0)  means  that  no  capsule 
was  produced,  or  if  a  capsule  was  produced  that  it  con- 
tained no  good  seed.  In  some  part  of  each  row  of  fig- 
ures in  each  compartment,  a  short  horizontal  line  may 
be  seen;  the  unions  above  this  line  were  made  in  1862, 
and  below  it  in  1863.  It  is  of  importance  to  observe 
this,  as  it  shows  that  the  same  general  result  was  ob- 
tained during  two  successive  years ;  but  more  especially 
because  1863  was  a  very  hot  and  dry  season,  and  the 
plants  had  occasionally,  to  be  watered.  This  did  not 
prevent  the  full  complement  of  seeds  being  produced 
from  the  more  fertile  unions;  but  it  rendered  the  less 
fertile  ones  even  more  sterile  than  they  otherwise  would 
have  been.  I  have  seen  striking  instances  of  this  fact 
in  making  illegitimate  and  legitimate  unions  with  Pri- 
mula; and  it  is  well  known  that  the  conditions  of  life 
must  be  highly  favourable  to  give  any  chance  of  suc- 
cess in  producing  hybrids  between  species  which  are 
crossed  with  difficulty. 


152    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


TABLE  23. — Long-styled  Form. 


Legitimate  union. 
13  flowers  fertilised  bythelongest 
stamens  of  the  mid-styled.     These 
stamens  equal  in  strength  the  pistil 
of  the  long-styled. 
Product  of  good  seed  in   each 

capsule. 

36  53 

81  0 

0  0 

0  0 

0  0 

0 
45 
41 

38  per  cent,  of  these  flowers 
yielded  capsules.  Each  capsule 
contained,  on  an  average,  51.2 


II. 

Legitimate  union. 
13  flowers  fertilised  bythelongest 
stamens  of  the  short-styled.   These 
stamens  equal  in  length  the  pistil 
of  the  long-styled. 
Product  of   good  seed  in  each 

capsule. 
159 
43 

96  poor  seed. 
103 
0 
0 


104 
119 


131 
118 


114 


84  per  cent,  of  these  flowers 
yielded  capsules.  Each  capsule 
contained,  on  an  average,  107.3 
seeds. 


III. 

Illegitimate  union. 
14  flowers  fertilised  by  the  short- 
est stamens  of  the  mid-styled. 
3  0 

0  0 

0  0 

0  0 

0  0 

0 

0  0 

0 
Too  sterile  for  any  average. 


IV. 

Illegitimate  union. 
12  flowers  fertilised  by  the  mid- 
length  stamens  of  the  short-styled. 
20  0 

0  0 

0  0 

0  0 

—  0 

0  0 

0 

Too  sterile  for  any  average. 


V. 

Illegitimate  union. 
15  flowers  fertilised  by  own-form 
mid-length  stamens. 

2  — 

10  0 

23  0 

0  0 

0  0 

0  0 

0  0 

0  0 

Too  sterile  for  any  average. 


VI. 

Illegitimate  union. 
15  flowers  fertilised  by  own-form 
shortest  stamens. 

4  — 

8  0 

4  0 

0  0 

0  0 

0  0 

0  0 

0  0 

Too  sterile  for  any  average. 


CHAP.  IV.  LYTHRUM  SALICAKIA.  153 

Besides  the  above  experiments,  I  fertilised  a  con- 
siderable number  of  long-styled  flowers  with  pollen, 
taken  by  a  camel's-hair  brush,  from  both  the  mid- 
length  and  shortest  stamens  of  their  own  form;  only 
5  capsules  were  produced,  and  these  yielded  on  an 
average  14.5  seeds.  In  1863  I  tried  a  much  better 
experiment:  a  long-styled  plant  was  grown  by  itself, 
miles  away  from  any  other  plant,  so  that  the  flowers 
could  have  received  only  their  own  two  kinds  of  pol- 
len. The  flowers  were  incessantly  visited  by  bees,  and 
their  stigmas  must  have  received  successive  applica- 
tions of  pollen  on  the  most  favourable  days  and  at  the 
most  favourable  hours:  all  who  have  crossed  plants 
know  that  this  highly  favours  fertilisation.  This  plant 
produced  an  abundant  crop  of  capsules;  I  took  by 
chance  20  capsules,  and  these  contained  seeds  in  num- 
ber as  follows: — 

20  20  35  21  19 

26  24  12  23  10 

7  30  27  29  13 

20  12  29  19  35 

This  gives  an  average  of  21.5  seeds  per  capsule.  As 
we  know  that  the  long-styled  form,  when  standing 
near  plants  of  the  other  two  forms  and  fertilised  by 
insects,  produces  on  an  average  93  seeds  per  capsule, 
we  see  that  this  form,  fertilised  by  its  own  two  pollens, 
yields  only  between  one-fourth  and  one-fifth  of  the  full 
number  of  seeds.  I  have  spoken  as  if  the  plant  had 
received  both  its  own  kinds  of  pollen,  and  this  is,  of 
course,  possible;  but,  from  the  enclosed  position  of  the 
shortest  stamens,  it  is  much  more  probable  that  the 
stigma  received  exclusively  pollen  from  the  mid- 
length  stamens;  and  this,  as  may  be  seen  in  com- 
partment V.  in  Table  23,  is  the  more  fertile  of  the  two 
self-unions. 
12 


154   HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


TABLE  24.— Mid-styled  Form. 


I. 

II. 

Legitimate  union. 

Legitimate  union. 

12  flowers  fertilised  by  the  mid- 

12  flowers  fertilised  by  the  mid- 

length  stamens  of  the  long-styled. 

length  stamens  of  the  short-styled. 

These  stamens  equal  in  length  the 

These  stamens  equal  in  length  the 

pistil  of  the  mid-styled. 

pistil  of  the  mid-styled. 

Product  of  good  seed  in  each 

Product  of  good  seed  in  each 

capsule. 

capsule. 

138                        122 

112                        109 

149                          50 

130                         143 

147                          151 

143                         124 

109                          119 

100                          145 

133                          138 

33                            12 

144                             0 

141 



104 

92  per  cent,  of  the  flowers  (pro- 

100  per   cent,    of  the    flowers 

bably  100  per  cent.)  yielded  cap- 

yielded  capsules.     Each   capsule 

sules.    Each  capsule  contained,  on 

contained,   on  an    average,   108.0 

an  average,  127.3  seeds. 

seeds  ;  or,  excluding  capsules  with 

less  than  20  seeds,  the  average  is 

116.7  seeds. 

III. 

IV. 

Illegitimate  union. 

Illegitimate  union. 

13  flowers  fertilised  by  the  short- 

15 flowers  fertilised  by  the  long- 

est stamens  of  the  long-styled. 

est  stamens  of  the  short-styled. 

83                    12 

130                        86 

0                    19 

115                       113 

r  seeds  small 

14                          29 

0                   851   and  poor. 

6                          17 

0 

2                        113 

44                     0 

9                          79 

44                      0 

128 

45                      0 

132                            0 

54    per    cent,    of    the    flowers 

93    per    cent,    of    the    flowers 

yielded   capsules.     Each   capsule 

yielded    capsules.      Each    capsule 

contained,    on   an   average,    47.4 

contained,    on   an    average,    69.5 

seeds;  or,  excluding  capsules  with 

seeds  ;  or,  excluding  capsules  with 

less  than  20  seeds,  the  average  is 

less  than  20  seeds,  the  average  is 

60.2  seeds. 

102.8. 

CHAP.  IV. 


LYTHRUM  SALICARIA. 


155 


TABLE  24. — Mid-styled  Form — continued. 


V. 

VI. 

Illegitimate  union. 

Illegitimate  union. 

12  flowers  fertilised  by  own-form 
longest  stamens. 

12  flowers  fertilised  by  own-form 
shortest  stamens. 

92                           0 

0                          0 

9                           0 

0                          0 

63                           0 

0                          0 

0 

—               •          0 

136?*                      0 

0                           0 

0                           0 

0                           0 

0 

0 

Excluding  the  capsule  with  136 
seeds,  25  per  cent,  of  the  flowers 

Not  one  flower  yielded  a  capsule. 

yielded  capsules,  and  each  capsule 

contained,    on    an    average,    54.6 

seeds  ;  or,  excluding  capsules  with 
less  than  20  seeds,  the  average  is 

77.5. 

Besides  the  experiments  in  the  above  table,  I  fer- 
tilised a  considerable  number  of  mid-styled  flowers  with 
pollen,  taken  by  a  camel's-hair  brush,  from  both  the 
longest  and  shortest  stamens  of  their  own  form:  only 
5  capsules  were  produced,  and  these  yielded  on  an 
average  11.0  seeds. 


*  I  have  hardly  a  doubt  that 
this  result  of  136  seeds  in  compart- 
ment V.  was  due  to  a  gross  error. 
The  flowers  to  be  fertilised  by 
their  own  longest  stamens  were 
first  marked  by  "white  thread," 
and  those  by  the  mid-length 
stamens  of  the  long-styled  form 
by  "white  silk;"  a  flower  fertil- 
ised in  the  latter  manner  would 
have  yielded  about  136  seeds,  and 
it  may  be  observed  that  one  such 
pod  is  missing,  viz.  at  the  bottom 
of  compartment  I.  Therefore  I 
have  hardly  any  doubt  that  I 
fertilised  a  flower  marked  with 
"  white  thread  "  as  if  it  had  been 
marked  with  "  white  silk."  With 
respect  to  the  capsule  which  yield- 
ed 92  seeds,  in  the  same  column 
with  that  which  yielded  136,  I  do 
not  know  what  to  think.  I  en- 


deavoured to  prevent  pollen  drop- 
ping from  an  upper  to  a  lower 
flower,  and  I  tried  to  remember  to 
wipe  the  pincers  carefully  after 
each  fertilisation  ;  but  in  making 
eighteen  different  unions,  some- 
times on  windy  days,  and  pestered 
by  bees  and  flies  buzzing  about, 
some  few  errors  could  hardly  be 
avoided.  One  day  I  had  to  keep 
a  third  man  by  me  all  the  time  to 
prevent  the  bees  visiting  the  un- 
covered plants,  for  in  a  few  sec- 
onds' time  they  might  have  done 
irreparable  mischief.  It  was  also 
extremely  difficult  to  exclude 
minute  Diptera  from  the  net.  In 
1862  I  made  the  great  mistake  of 
placing  a  mid-styled  and  a  long- 
styled  under  the  same  huge  net : 
in  1863  I  avoided  this  error. 


156    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


TABLE  25. — Short-styled  Form. 


I. 

II. 

Legitimate  union. 

Legitimate  union. 

12  flowers  fertilised  by  the  short- 

13 flowers  fertilised  by  the  short- 

est stamens    of   the    long-styled. 

est    stamens    of    the    mid-styled. 

These  stamens  equal  in  length  the 
pistil  of  the  short-styled. 

These  stamens  equal  in  length  the 
pistil  of  the  short-styled. 

69                        56 

93                        69 

61                        88 

77                        69 

88                       112 

48                         53 

66                       111 

43                            9 

0                          62 

0                           0 

0                        100 

0                           0 

— 

—                           0 

83    per    cent,    of    the    flowers 

61    per    cent,    of    the    flowers 

yielded    capsules.     Each    capsule 
contained,    on   an   average,    81.3 

yielded    capsules.      Each    capsule 
contained,    on    an    average,    64.6 

seeds. 

seeds. 

III. 

IV. 

Illegitimate  union. 

Illegitimate  union. 

10  flowers  fertilised  by  the  mid- 
length  stamens  of  the  long-styled. 

10  flowers  fertilised  by  the  long- 
est stamens  of  the  mid-styled. 

0                        14 

0                          0 

0                          0 

0                          0 

0                          0 

0                           0 

0                          0 

0                            0 

0 

0 

23 

0 

Too  sterile  for  any  average. 

Too  sterile  for  any  average. 

V. 

VI. 

Illegitimate  union. 

Illegitimate  union. 

10  flowers  fertilised  by  own-form 
longest  stamens. 

10  flowers  fertilised  by  own-form 
mid-length  stamens. 

0                           0 

64?*                     0 

0                           0 

0                          0 

0                           0 

0                          0 

0 

—                          0 

0                          0 

21                          0 

0 

9 

Too  sterile  for  any  average. 

Too  sterile  for  any  average. 

*  I  suspect  that  by  mistake  I  to  be  thus  fertilised  were  marked 

fertilised  this  flower  in  compart-  with  black  silk  ;  those  with  pollen 

ment  VI.   with  pollen  from  the  from  the  mid-length   stamens  of 

shortest  stamens  of  the  long-styled  the  short-styled  with  black  thread ; 

form,  and   it  would   then    have  and   thus   probably  the  mistake 

yielded  about  64  seeds.    Flowers  arose. 


CHAP.  IV.  LYTHRUM  SALICARIA.  15? 

Besides  the  experiments  in  the  table,  I  fertilised  a 
number  of  flowers  without  particular  care  with  their 
own  two  kinds  of  pollen,  but  they  did  not  produce  a 
single  capsule. 

Summary  of  the  Results. 

Long-styled  form. — Twenty-six  flowers  fertilised 
legitimately  by  the  stamens  of  corresponding  length, 
borne  by  the  mid-  and  short-styled  forms,  yielded  61.5 
per  cent,  of  capsules,  which  contained  on  an  average 
89.7  seeds. 

Twenty-six  long-styled  flowers  fertilised  illegiti- 
mately by  the  other  stamens  of  the  mid-  and  short- 
styled  forms  yielded  only  two  very  poor  capsules. 

Thirty  long-styled  flowers  fertilised  illegitimately  by 
their  own-form  two  sets  of  stamens  yielded  only  eight 
very  poor  capsules;  but  long-styled  flowers  fertilised 
by  bees  with  pollen  from  their  own  stamens  produced 
numerous  capsules  containing  on  an  average  21.5 
seeds. 

Mid-styled  form. — Twenty-four  flowers  legitimately 
fertilised  by  the  stamens  of  corresponding  length, 
borne  by  the  long-  and  short-styled  forms,  yielded  96 
(probably  100)  per  cent,  of  capsules,  which  contained 
(excluding  one  capsule  with  12  seeds)  on  an  average 
117.2  seeds. 

Fifteen  mid-styled  flowers  fertilised  illegitimately 
by  the  longest  stamens  of  the  short-styled  form  yielded 
93  per  cent,  of  capsules,  which  (excluding  four  cap- 
sules with  less  than  20  seeds)  contained  on  an  average 
102.8  seeds. 

Thirteen  mid-styled  flowers  fertilised  illegitimately 
by  the  mid-length  stamens  of  the  long-styled  form 
yielded  54  per  cent,  of  capsules,  which  (excluding 
one  with  19  seeds)  contained  on  an  average  60.2  seeds. 


158    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


Twelve  mid-styled  flowers  fertilised  illegitimately 
by  their  own- form  longest  stamens  yielded  25  per  cent, 
of  capsules,  which  (excluding  one  with  9  seeds)  con- 
tained on  an  average  77.5  seeds. 

Twelve  mid-styled  flowers  fertilised  illegitimately 
by  their  own-form  shortest  stamens  yielded  not  a  single 
capsule. 

Short-styled  form. — Twenty-five  flowers  fertilised 
legitimately  by  the  stamens  of  corresponding  length, 
borne  by  the  long-  and  mid-styled  forms,  yielded  72 
per  cent,  of  capsules,  which  (excluding  one  capsule  with 
only  nine  seeds)  contained  on  an  average  70.8  seeds. 

Twenty  short-styled  flowers  fertilised  illegitimately 
by  the  other  stamens  of  the  long-  and  mid-styled  forms 
yielded  only  two  very  poor  capsules. 

Twenty  short-styled  flowers  fertilised  illegitimately 
by  their  own  stamens  yielded  only  two  poor  (or  per- 
haps three)  capsules. 

If  we  take  all  six  legitimate  unions  together,  and 
all  twelve  illegitimate  unions  together,  we  get  the  fol- 
lowing results : — 

TABLE  26. 


Katun 

of  Union. 

Number 
of 
Flowers 
fertilised. 

Number 
of 
Capsule, 
produced. 

Average 
Number  of 
Seeds  per 
Capsu.e. 

Averaee  Num- 
ber of  Seeds 
per  Flower 
fertilised. 

The       six 

legitimate  ) 

75 

56 

96.29 

71.89 

' 

The  twelve 
unions  . 

illegitimate  ) 
j 

146 

36 

44.72 

11.03 

Therefore  the  fertility  of  the  legitimate  unions  to  that 
of  the  illegitimate,  as  judged  by  the  proportion  of  the 
fertilised  flowers  which  yielded  capsules,  is  as  100  to 
33;  and  judged  by  the  average  number  of  seeds  per 
capsule,  as  100  to  46. 


CHAP.  IV.  LYTHRUM  SALICARIA.  15£ 

From  this  summary  and  the  several  foregoing  tables 
we  see  that  it  is  only  pollen  from  the  longest  stamens 
which  can  fully  fertilise  the  longest  pistil;  only  that 
from  the  mid-length  stamens,  the  mid- length  pistil; 
and  only  that  from  the  shortest  stamens,  the  shortest 
pistil.  And  now  we  can  comprehend  the  meaning  of 
the  almost  exact  correspondence  in  length  between 
the  pistil  in  each  form  and  a  set  of  six  stamens 
in  two  of  the  other  forms;  for  the  stigma  of  each 
form  is  thus  rubbed  against  that  part  of  the  insect's 
body  which  becomes  charged  with  the  proper  pollen. 
It  is  also  evident  that  the  stigma  of  each  form, 
fertilised  in  three  different  ways  with  pollen  from 
the  longest,  mid-length,  and  shortest  stamens,  is  acted 
on  very  differently,  and  conversely,  that  the  pollen  from 
the  twelve  longest,  twelve  mid-length,  and  twelve 
shortest  stamens  acts  very  differently  on  each  of  the 
three  stigmas;  so  that  there  are  three  sets  of  female 
and  of  male  organs.  Moreover  in  most  cases  the  six 
stamens  of  each  set  differ  somewhat  in  their  fertilising 
power  from  the  six  corresponding  ones  in  one  of  the 
other  forms.  We  may  further  draw  the  remarkable 
conclusion  that  the  greater  the  inequality  in  length 
between  the  pistil  and  the  set  of  stamens,  the  pollen 
of  which  is  employed  for  its  fertilisation,  by  so  much 
is  the  sterility  of  the  union  increased.  There  are  no 
exceptions  to  this  rule.  To  understand  what  follows 
the  reader  should  look  at  Tables  23,  24  and  25,  and 
to  the  diagram  Fig.  10,  p.  139.  In  the  long-styled  form 
the  shortest  stamens  obviously  differ  in  length  from 
the  pistil  to  a  greater  degree  than  do  the  mid-length 
stamens;  and  the  capsules  produced  by  the  use  of 
pollen  from  the  shortest  stamens  contain  fewer  seeds 
than  those  produced  by  the  pollen  from  the  mid- 
length  stamens.  The  same  result  follows  with  the 


160    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

long-styled  form,  from  the  use  of  the  pollen  of  the 
shortest  stamens  of  the  mid-styled  form  and  of  the 
mid-length  stamens  of  the  short-styled  form.  The 
same  rule  also  holds  good  with  the  mid-styled  and 
short-styled  forms,  when  illegitimately  fertilised  with 
pollen  from  the  stamens  more  or  less  unequal  in 
length  to  their  pistils.  Certainly  the  difference  in 
sterility  in  these  several  cases  is  slight;  but,  as  far  as 
we  are  enabled  to  judge,  it  always  increases  with  the 
increasing  inequality  of  length  between  the  pistil  and 
the  stamens  which  are  used  in  each  case. 

The  correspondence  in  length  between  the  pistil  in 
each  form  and  a  set  of  stamens  in  the  other  two  forms, 
is  probably  the  direct  result  of  adaptation,  as  it  is  of 
high  service  to  the  species  by  leading  to  full  and 
legitimate  fertilisation.  But  the  rule  of  the  increased 
sterility  of  the  illegitimate  unions  according  to  the 
greater  inequality  in  length  between  the  pistils  and 
stamens  employed  for  the  union  can  be  of  no  service. 
With  some  heterostyled  dimorphic  plants  the  dif- 
ference of  fertility  between  the  two  illegitimate  unions 
appears  at  first  sight  to  be  related  to  the  facility  of 
self- fertilisation ;  so  that  when  from  the  position  of 
the  parts  the  liability  in  one  form  to  self-fertilisation 
is  greater  than  in  the  other,  a  union  of  this  kind 
has  been  checked,  by  having  been  rendered  the 
more  sterile  of  the  two.  But  this  explanation  does 
not  apply  to  Lythrum;  thus  the  stigma  of  the  long- 
styled  form  is  more  liable  to  be  illegitimately  fer- 
tilised with  pollen  from  its  own  mid-length  stamens, 
or  with  pollen  from  the  mid-length  stamens  of  the 
short-styled  form,  than  by  its  own  shortest  stamens 
or  those  of  the  mid-styled  form;  yet  the  two  former 
unions,  which  it  might  have  been  expected  would 
have  been  guarded  against  by  increased  sterility, 


CHAP.  IV.  LYTHRUM  SALICAEIA.  161 

are  much  less  sterile  than  the  other  two  unions 
which  are  much  less  likely  to  be  effected.  The 
same  relation  holds  good  even  in  a  more  striking 
manner  with  the  mid-styled  form,  and  with  the  short- 
styled  form  as  far  as  the  extreme  sterility  of  all  its 
illegitimate  unions  allows  of  any  comparison.  We 
are  led,  therefore,  to  conclude  that  the  rule  of  in- 
creased sterility,  in  accordance  with  increased  in- 
equality in  length  between  the  pistils  and  stamens, 
is  a  purposeless  result,  incidental  on  those  changes 
through  which  the  species  has  passed  in  acquiring  cer- 
tain characters  fitted  to  ensure  the  legitimate  fertilisa- 
tion of  the  three  forms. 

Another  conclusion  which  may  be  drawn  from 
Tables  23,  24,  and  25,  even  from  a  glance  at  them, 
is  that  the  mid-styled  form  differs  from  both  the 
others  in  its  much  higher  capacity  for  fertilisation 
in  various  ways.  Not  only  did  the  twenty-four  flowers 
legitimately  fertilised  by  the  stamens  of  corresponding 
lengths,  all,  or  all  but  one,  yield  capsules  rich  in 
seed;  but  of  the  other  four  illegitimate  unions,  that 
by  the  longest  stamens  of  the  short-styled  form  was 
highly  fertile,  though  less  so  than  the  two  legitimate 
unions,  and  that  by  the  mid-length  stamens  of  the 
long-styled  form  was  fertile  to  a  considerable  degree; 
the  remaining  two  illegitimate  unions,  namely,  with 
this  form's  own  pollen,  were  sterile,  but  in  different 
degrees.  So  that  the  mid-styled  form,  when  fertilised 
in  the  six  different  possible  methods,  evinces  five 
grades  of  fertility.  By  comparing  compartments  III. 
and  VI.  in  Table  24  we  may  see  that  the  action  of 
the  pollen  from  the  shortest  stamens  of  the  long-styled 
and  mid-styled  forms  is  widely  different ;  in  the  one 
case  above  half  the  fertilised  flowers  yielded  capsules 
containing  a  fair  number  of  seeds;  in  the  other  case 


162    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

not  one  capsule  was  produced.  So,  again,  the  green, 
large-grained  pollen  from  the  longest  stamens  of 
the  short-styled  and  mid-styled  forms  (in  compart- 
ments IV.  and  V.)  is  widely  different.  In  both  these 
cases  the  difference  in  action  is  so  plain  that  it  cannot 
be  mistaken,  but  it  can  be  corroborated.  If  we  look 
to  Table  25  to  the  legitimate  action  of  the  shortest 
stamens  of  the  long-  and  mid-styled  forms  on  the 
short-styled  form,  we  again  see  a  similar  but  slighter 
difference,  the  pollen  of  the  shortest  stamens  of  the 
mid-styled  form  yielding  a  smaller  average  of  seed 
during  the  two  years  of  1862  and  1863  than  that  from 
the  shortest  stamens  of  the  long-styled  form.  Again, 
if  we  look  to  Table  23,  to  the  legitimate  action  on 
the  long-styled  form  of  the  green  pollen  of  the  two 
sets  of  longest  stamens,  we  shall  find  exactly  the  same 
result,  viz.  that  the  pollen  from  the  longest  stamens  of 
the  mid-styled  form  yielded  during  both  years  fewer 
seeds  than  that  from  the  longest  stamens  of  the 
short-styled  form.  Hence  it  is  certain  that  the  two 
kinds  of  pollen  produced  by  the  mid-styled  form  are 
less  potent  than  the  two  similar  kinds  of  pollen  pro- 
duced by  the  corresponding  stamens  of  the  other  two 
forms. 

In  close  connection  with  the  lesser  potency  of  the 
two  kinds  of  pollen  of  the  mid-styled  form  is  the  fact 
that,  according  to  H.  Miiller,  the  grains  of  both  are 
a  little  less  in  diameter  than  the  corresponding  grains 
produced  by  the  other  two  forms.  Thus  the  grains 
from  the  longest  stamens  of  the  mid-styled  form  are 
9  to  10,  whilst  those  from  the  corresponding  stamens 
of  the  short-styled  form  are  9£  to  10£  in  diameter. 
So,  again,  the  grains  from  the  shortest  stamens  of  the 
mid-styled  are  6,  whilst  those  from  the  corresponding 
stamens  of  the  long-styled  are  6  to  6£  in  diameter. 


CHAP.  IV.  LYTHRUM  SALICAEIA.  163 

It  would  thus  appear  as  if  the  male  organs  of  the 
mid-styled  form,  though  not  as  yet  rudimentary,  were 
tending  in  this  direction.  On  the  other  hand,  the 
female  organs  of  this  form  are  in  an  eminently  efficient 
state,  for  the  naturally  fertilised  capsules  yielded  a 
considerably  larger  average  number  of  seeds  than 
those  of  the  other  two  forms — almost  every  flower 
which  was  artificially  fertilised  in  a  legitimate  manner 
produced  a  capsule — and  most  of  the  illegitimate 
unions  were  highly  productive.  The  mid-styled  form 
thus  appears  to  be  highly  feminine  in  nature;  and  al- 
though, as  just  remarked,  it  is  impossible  to  consider 
its  two  well-developed  sets  of  stamens  which  produce 
an  abundance  of  pollen  as  being  in  a  rudimentary 
condition,  yet  we  can  hardly  avoid  connecting  as 
balanced  the  higher  efficiency  of  the  female  organs  in 
this  form  with  the  lesser  efficiency  and  lesser  size  of  its 
two  kinds  of  pollen-grains.  The  whole  case  appears 
to  me  a  very  curious  one. 

It  may  be  observed  in  Tables  23  to  25  that  some 
of  the  illegitimate  unions  yielded  during  neither  year 
a  single  seed ;  but,  judging  from  the  long-styled  plants, 
it  is  probable,  if  such  unions  were  to  be  effected  re- 
peatedly by  the  aid  of  insects  under  the  most  favour- 
able conditions,  some  few  seeds  would  be  produced  in 
every  case.  Anyhow,  it  is  certain  that  in  all  twelve 
illegitimate  unions  the  pollen-tubes  penetrated  the 
stigma  in  the  course  of  eighteen  hours.  At  first  I 
thought  that  two  kinds  of  pollen  placed  together  on 
the  same  stigma  would  perhaps  yield  more  seed  than 
one  kind  by  itself;  but  we  have  seen  that  this  is  not 
so  with  each  form's  own  two  kinds  of  pollen;  nor  is  it 
probable  in  any  case,  as  I  occasionally  got,  by  the  use 
of  a  single  kind  of  pollen,  fully  as  many  seeds  as  a 
capsule  naturally  fertilised  ever  produces.  Moreover 


164    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

the  pollen  from  a  single  anther  is  far  more  than  suffi- 
cient to  fertilise  fully  a  stigma;  since,  in  this  as  with 
so  many  other  plants,  more  than  twelve  times  as  much 
of  each  kind  of  pollen  is  produced  as  is  necessary  to 
ensure  the  full  fertilisation  of  each  form.  From  the 
dusted  condition  of  the  bodies  of  the  bees  which  I 
caught  on  the  flowers,  it  is  probable  that  pollen  of 
various  kinds  is  often  deposited  on  all  three  stigmas; 
but  from  the  facts  already  given  with  respect  to  the 
two  forms  of  Primula,  there  can  hardly  be  a  doubt 
that  pollen  from  the  stamens  of  corresponding  length 
placed  on  a  stigma  would  be  prepotent  over  any  other 
kind  of  pollen  and  obliterate  its  effects, — even  if  the 
latter  had  been  placed  on  the  stigma  some  hours  pre- 
viously. 

Finally,  it  has  now  been  shown  that  Lythrum  sali- 
caria  presents  the  extraordinary  case  of  the  same 
species  bearing  three  females,  different  in  structure  and 
function,  and  three  or  even  five  sets  (if  minor  differ- 
ences are  considered)  of  males;  each  set  consisting  of 
half-a-dozen,  which  likewise  differ  from  one  another  in 
structure  and  function. 

Lythrum  Grcefferi. — I  have  examined  numerous  dried 
flowers  of  this  species,  each  from  a  separate  plant,  sent  me 
from  Kew.  Like  L.  salicaria,  it  is  trimorphic,  and  the 
three  forms  apparently  occur  in  about  equal  numbers.  In 
the  long-styled  form  the  pistil  projects  about  one-third  of 
the  length  of  the  calyx  beyond  its  mouth,  and  is  therefore 
relatively  much  shorter  than  in  L.  salicaria;  the  globose 
and  hirsute  stigma  is  larger  than  that  of  the  other  two 
forms;  the  six  mid-length  stamens,  which  are  graduated 
in  length,  have  their  anthers  standing  close  above  and  close 
beneath  the  mouth  of  the  calyx;  the  six  shortest  stamens 
rise  rather  above  the  middle  of  the  calyx.  In  the  mid- 
styled  form  the  stigma  projects  just  above  the  mouth  of 
the  calyx,  and  stands  almost  on  a  level  with  the  mid-length 
stamens  of  the  long-  and  short-styled  forms ;  its  own  long- 


CHAP.  IV.  LYTHRUM  HYSSOPIFOLIA.  165 

est  stamens  project  well  above  the  mouth  of  the  calyx,  and 
stand  a  little  above  the  level  of  the  stigma  of  the  long- 
styled  form.  In  short,  without  entering  on  further  details, 
there  is  a  close  general  correspondence  in  structure  be- 
tween this  species  and  L.  salicaria,  but  with  some  differ- 
ences in  the  proportional  lengths  of  the  parts.  The  fact 
of  each  of  the  three  pistils  having  two  sets  of  stamens  of 
corresponding  lengths,  borne  by  the  two  other  forms,  comes 
out  conspicuously.  In  the  mid-styled  form  the  pollen- 
grains  from  the  longest  stamens  are  nearly  double  the  di- 
ameter of  those  from  the  shortest  stamens ;  so  that  there  is 
a  greater  difference  in  this  respect  than  in  L.  salicaria. 
In  the  long-styled  form,  also,  the  difference  in  diameter  be- 
tween the  pollen-grains  of  the  mid-length  and  shortest  sta- 
mens is  greater  than  in  L.  salicaria.  These  comparisons, 
however,  must  be  received  with  caution,  as  they  were  made 
on  specimens  soaked  in  water,  after  having  been  long  kept 
dry. 

Lythrum  thymifolia. — This  form,  according  to  Vauch- 
er,*  is  dimorphic,  like  Primula,  and  therefore  presents  only 
two  forms.  I  received  two  dried  flowers  from  Kew,  which 
consisted  of  the  two  forms;  in  one  the  stigma  projected 
far  beyond  the  calyx,  in  the  other  it  was  included  within 
the  calyx ;  in  this  latter  form  the  style  was  only  one-fourth 
of  the  length  of  that  in  the  other  form.  There  are  only 
six  stamens ;  these  are  somewhat  graduated  in  length,  and 
their  anthers  in  the  short-styled  form  stand  a  little  above 
the  stigma,  but  yet  by  no  means  equal  in  length  the  pistil 
of  the  long-styled  form.  In  the  latter  the  stamens  are 
rather  shorter  than  those  in  the  other  form.  The  six  sta- 
mens alternate  with  the  petals,  and  therefore  correspond 
homologically  with  the  longest  stamens  of  L.  salicaria 
and  L.  Grcefferi. 

Lythrum  hyssopifolia. — This  species  is  said  by  Vauch- 
er,  but  I  believe  erroneously,  to  be  dimorphic.  I  have 
examined  dried  flowers  from  twenty-two  separate  plants 
from  various  localities,  sent  to  me  by  Mr.  Hewett  C.  Wat- 
son, Professor  Babington,  and  others.  These  were  all 
essentially  alike,  so  that  the  species  cannot  be  heterostyled. 
The  pistil  varies  somewhat  in  length,  but  when  unusually 


*  '  Hist.  Phys.  des  Plantes  d' Europe,'  torn.  ii.  (1841),  pp.  369,  371. 


166    HETEEOSTYLED  TEIMOEPHIC  PLANTS.    CHAP.  IV. 

long,  the  stamens  are  likewise  generally  long;  in  the  bud 
the  stamens  are  short;  and  Vaucher  was  perhaps  thus  de- 
ceived. There  are  from  six  to  nine  stamens  graduated  in 
length.  The  three  stamens,  which  vary  in  being  either 
present  or  absent,  correspond  with  the  six  shorter  stamens 
of  L.  salicaria  and  with  the  six  which  are  always  absent  in 
L.  thy mif olia.  The  stigma  is  included  within  the  calyx, 
and  stands  in  the  midst  of  the  anthers,  and  would  gen- 
erally be  fertilised  by  them ;  but  as  the  stigma  and  anthers 
are  upturned,  and  as,  according  to  Vaucher,  there  is  a  pas- 
sage left  in  the  upper  side  of  the  flower  to  the  nectary, 
there  can  hardly  be  a  doubt  that  the  flowers  are  visited 
by  insects,  and  would  occasionally  be  cross-fertilised  by 
them,  as  surely  as  the  flowers  of  the  short-styled  L.  sali- 
caria, the  pistil  of  which  and  the  corresponding  stamens 
in  the  other  two  forms  closely  resemble  those  of  L.  hys- 
sopifolia.  According  to  Vaucher  and  Lecoq,*  this  species, 
which  is  an  annual,  generally  grows  almost  solitarily, 
whereas  the  three  preceding  species  are  social ;  and  this  fact 
alone  would  almost  have  convinced  me  that  L.  hyssopifolia 
was  not  heterostyled,  as  such  plants  cannot  habitually  live 
isolated  any  better  than  one  sex  of  a  dioecious  species. 

We  thus  see  that  within  this  genus  some  species  are 
heterostyled  and  trimorphic;  one  apparently  heterostyled 
and  dimorphic,  and  one  homostyled. 

Nescea  verticillata. — I  raised  a  number  of  plants  from 
seed  sent  me  by  Professor  Asa  Gray,  and  they  presented 
three  forms.  These  differed  from  one  another  in  the  pro- 
portional lengths  of  their  organs  of  fructification  and  in 
all  respects,  in  very  nearly  the  same  way  as  the  three  forms 
of  Lythrum  Grcefferi.  The  green-pollen  grains  from  the 
longest  stamens,  measured  along  their  longer  axis  and  not 
distended  with  water,  were  T^f?  of  an  inch  in  length ;  those 
from  the  mid-length  stamens  rinsir,  and  those  from  the 
shortest  stamens  -ri'-jnr  of  an  inch.  So  that  the  largest  pol- 
len-grains are  to  the  smallest  in  diameter  as  100  to  65. 
This  plant  inhabits  swampy  ground  in  the  United  States. 
According  to  Fritz  Miiller,  f  a  species  of  this  genus  in  St. 
Catharina,  in  Southern  Brazil,  is  homostyled. 


*  'Geograph.  Bot.  de  1'Europe,'  torn,  vi.,  1857,  p.  157. 
t  'Bot.  Zeitung,'  1868,  p.  112. 


CHAP.  IV.  LAGERSTRCEMIA  INDICA.  16? 

Lagerstrcemia  Indica. — This  plant,  a  member  of  the 
Lythracese,  may  perhaps  be  heterostyled,  or  may  formerly 
have  been  so.  It  is  remarkable  from  the  extreme  variability 
of  its  stamens.  On  a  plant,  growing  in  my  hothouse,  the 
flowers  included  from  nineteen  to  twenty-nine  short  sta- 
mens with  yellow  pollen,  which  correspond  in  position 
with  the  shortest  stamens  of  Ly thrum;  and  from  one  to 
five  (the  latter  number  being  the  commonest)  very  long 
stamens,  with  thick  flesh-coloured  filaments  and  green 
pollen,  corresponding  in  position  with  the  longest  stamens 
of  Lythrum.  In  one  flower,  two  of  the  long  stamens  pro- 
duced green,  while  a  third  produced  yellow  pollen,  although 
the  filaments  of  all  three  were  thick  and  flesh-coloured. 
In  an  anther  of  another  flower,  one  cell  contained  green 
and  the  other  yellow  pollen.  The  green  and  yellow  pollen- 
grains  from  the  stamens  of  different  length  are  of  the  same 
size.  The  pistil  is  a  little  bowed  upwards,  with  the  stigma 
seated  between  the  anthers  of  the  short  and  long  stamens, 
so  that  this  plant  was  mid-styled.  Eight  flowers  were  fer- 
tilised with  green  pollen,  and  six  with  yellow  pollen,  but 
not  one  set  fruit.  This  latter  fact  by  no  means  proves  that 
the  plant  is  heterostyled,  as  it  may  belong  to  the  class  of 
self -sterile  species.  Another  plant  growing  in  the  Botanic 
Gardens  at  Calcutta,  as  Mr.  J.  Scott  informs  me,  was  long- 
styled,  and  it  was  equally  sterile  with  its  own  pollen ;  whilst 
a  long-styled  plant  of  L,  regince,  though  growing  by  itself, 
produced  fruit.  I  examined  dried  flowers  from  two  plants 
of  L.  parviflora,  both  of  which  were  long-styled,  and  they 
differed  from  L.  Indica  in  having  eight  long  stamens  with 
thick  filaments,  and  a  crowd  of  shorter  stamens.  Thus  the 
evidence  whether  L.  Indica  is  heterostyled  is  curiously  con- 
flicting; the  unequal  number  of  the  short  and  long  sta- 
mens, their  extreme  variability,  and  especially  the  fact  of 
their  pollen-grains  not  differing  in  size,  are  strongly  op- 
posed to  this  belief:  on  the  other  hand,  the  difference  in 
length  of  the  pistils  in  two  of  the  plants,  their  sterility 
with  their  own  pollen,  and  the  difference  in  length  and 
structure  of  the  two  sets  of  stamens  in  the  same  flower,  and 
in  the  colour  of  their  pollen,  favour  the  belief.  We  know 
that  when  plants  of  any  kind  revert  to  a  former  condition, 
they  are  apt  to  be  highly  variable,  and  the  two  halves  of  the 
same  organ  sometimes  differ  much,  as  in  the  case  of  the 


168    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

above-described  anther  of  the  Lagerstroemia ;  we  may  there- 
fore suspect  that  this  species  was  once  heterostyled,  and 
that  it  still  retains  traces  of  its  former  state,  together  with 
a  tendency  to  revert  more  completely  to  it.  It  deserves 
notice,  as  bearing  on  the  nature  of  Lagerstroemia,  that  in 
Lythrum  hyssopifolia,  which  is  a  homostyled  species,  some 
of  the  shorter  stamens  vary  in  being  either  present  or 
absent,  and  that  these  stamens  are  altogether  absent  in 
L.  thymifolia.  In  another  genus  of  the  Lythracese,  namely 
Cuphea,  three  species  raised  by  me  from  seed  certainly 
were  homostyled;  nevertheless  their  stamens  consisted  of 
two  sets  differing  in  length  and  in  the  colour  and  thickness 
of  their  filaments,  but  not  in  the  size  or  colour  of  their  pol- 
len-grains ;  so  that  they  thus  far  resembled  the  stamens  of 
Lagerstrcemia.  I  found  that  Cuphea  purpurea  was  highly 
fertile  with  its  own  pollen  when  artificially  aided,  but 
sterile  when  insects  were  excluded.* 


OXALIS  (GEBANIACE.E). 

In  1863  Mr.  Eoland  Trimen  wrote  to  me  from  the 
Cape  of  Good  Hope  that  he  had  there  found  species  of 
Oxalis  which  presented  three  forms;  and  of  these  he 
enclosed  drawings  and  dried  specimens.  Of  one  species 
he  collected  43  flowers  from  distinct  plants,  and  they 
consisted  of  10  long-styled,  12  mid-styled,  and  21 
short-styled.  Of  another  species  he  collected  13  flowers, 
consisting  of  3  long-styled,  7  mid-styled,  and  3  short- 


*  Mr.  Spence  informs  me  that  some  specimens  of  Mollia  lepidota 

in  several  species   of  the  genus  and  speciosa  from  Kew,  but  could 

Mollia  (Tiliacese)  which    he  col-  not  make  out  that  their  pistils 

lected    in    South    America,    the  differed    in    length    in    different 

stamens  of  the  five  outer  cohorts  plants ;  and  in  all    those  which 

have  purplish  filaments  and  green  I    examined     the    stigma    stood 

pollen,  whilst  the  stamens  of  the  close      beneath     the     uppermost 

five  inner    cohorts    have  yellow  anthers.     The  numerous  stamens 

pollen.      He  therefore   suspected  are  graduated  in  length,  and  the 

that  these  species  might  prove  to  pollen-grains  from  the  longest  and 

be  heterostyled  and  trimorphic  :  shortest  ones  did  not  present  any 

but  he  did  not  notice  the  length  of  marked   difference    in    diameter, 

the  pistils.    In  the  allied  Luhea  Therefore  these  species  do  not  ap- 

the  outer  purplish   stamens   are  pear  to  be  heterostyled. 
destitute  of  anthers.    I  procured 


CHAP.  IV.  OXALIS.  1C9 

styled.  In  1866  Professor  Hildebrand  proved,*  by  an 
examination  of  the  specimens  in  several  herbaria,  that 
20  species  are  certainly  heterostyled  and  trimorphic,  and 
51  others  almost  certainly  so.  He  also  made  some  in- 
teresting observations  on  living  plants  belonging  to 
one  form  alone;  for  at  that  time  he  did  not  possess 

Fig.  11. 


Long-styled.  Mid-styled.  Short-styled. 

OXALIS  SPKCIOSA  (with  the  petals  removed). 

B  S  S,  stigmas.     The  dotted  lines  with  arrows  show  which  pollen  must 
be  carried  to  the  stigmas  for  legitimate  fertilisation. 

the  three  forms  of  any  living  species.  During  the 
years  1864  to  1868  I  occasionally  experimented  on 
Oxalis  speciosa,  but  until  now  have  never  found  time 
to  publish  the  results.  In  1871  Hildebrand  published 
an  admirable  paperf  in  which  he  shows  in  the  case  of 
two  species  of  Oxalis,  that  the  sexual  relations  of  the 
three  forms  are  nearly  the  same  as  in  Lythrum  sali- 
caria.  I  will  now  give  an  abstract  of  his  observa- 
tions, and  afterwards  of  my  own  less  complete  ones. 
I  may  premise  that  in  all  the  species  seen  by  me,  the 
stigmas  of  the  five  straight  pistils  of  the  long-styled 
form  stand  on  a  level  with  the  anthers  of  the  longest 


*  '  Monatsber.     der   Akad.    der  forms  at  p.  42  of  his  '  Geschlechter- 

Wiss.   Berlin,'  1866,  pp.  352,  372.  VertheilunR.'  &c.,  1867. 

He  gives  drawings  of  the  three  f  'Bot.Zeitung'  1871,  pp.  416,  432. 
13 


170    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

stamens  in  the  two  other  forms.  In  the  mid-styled 
form,  the  stigmas  pass  out  between  the  filaments  of 
the  longest  stamens  (as  in  the  short-styled  form  of 
Linum) ;  and  they  stand  rather  nearer  to  the  upper 
anthers  than  to  the  lower  ones.  In  the  short-styled 
form,  the  stigmas  also  pass  out  between  the  filaments 
nearly  on  a  level  with  the  tips  of  the  sepals.  The 
anthers  in  this  latter  form  and  in  the  mid-styled  rise 
to  the  same  height  as  the  corresponding  stigmas  in  the 
other  two  forms. 

Oxalis  Valdiviana. — This  species,  an  inhabitant  of 
the  west  coast  of  South  America,  bears  yellow  flowers. 
Hildebrand  states  that  the  stigmas  of  the  three  forms 
do  not  differ  in  any  marked  manner,  but  that  the  pistil 
of  the  short-styled  form  alone  is  destitute  of  hairs. 
The  diameters  of  the  pollen-grains  are  as  follows : — 


From  the  longest  stamens  of  short-styled 8  to  9 

mid-length     "  "  7  "  8 

longest  stamens  of  mid-styled 8 

shortest          "  "  6 

mid-length  stamens  of  long-styled    ....  7 

shortest          "  6 

Therefore  the  extreme  difference  in  diameter  is  as  8.5 
to  6,  or  as  100  to  71.  The  results  of  Hildebrand's  ex- 
periments are  given  in  the  following  table,  drawn  up 
in  accordance  with  my  usual  plan.  He  fertilised  each 
form  with  pollen  from  the  two  sets  of  anthers  of  the 
same  flower,  and  likewise  from  flowers  on  distinct 
plants  belonging  to  the  same  form;  but  the  effects  of 
these  two  closely  allied  kinds  of  fertilisation  differ  so 
little  that  I  have  not  kept  them  distinct. 


CHAP.  IV. 


OXALIS  VALDIVIANA. 


171 


TABLE  27. 
Oxalis  Valdiviana  (from  Hildebrand). 


Cspsulei 
produced. 


Long-styled  form,   by  pollen  of  longest) 
stamens   of  short-styled.      Legitimate  f        28  28 

union , 

Long-styled  form,   by  pollen  of  longest) 
stamens    of    mid-styled.       Legitimate  \        21  21 

union _ 

Long-styled  form,  by  pollen  of  own  and 
own-form  mid-length  stamens.    Illegiti-  ^        40 
mate  union ^ 

Long-styled  form,  by  pollen  of  own  and  ) 
own-form  shortest    stamens.      Illegiti-  >        26  0 

mate  union J 

Long-styled  form,  by  pollen  of  shortest ) 
stamens  of  short-styled.      Illegitimate  >        16  1 

union J 

Long-styled  form,  by  pollen  of  shortest) 
stamens    of   mid-styled.      Illegitimate  >         9  0 

union J 

Mid-styled  form,  by  pollen  of  mid-length 
stamens  of  long-styled.  Legitimate 
union 

Mid-styled  form,  by  pollen  of  mid-length  ) 
stamens   of  short-styled.      Legitimate  >        23  23 

union J 

Mid-styled  form,  by  pollen  of  own  and 
own-form  longest  stamens.  Illegitimate  )•  52  0 

union , 

Mid-styled  form,  by  pollen  of  own  and) 
own-form  shortest  stamens.  Illegitimate  f        30  1 

union 

Mid-styled  form,  by  pollen  of  shortest' 
stamens  of  long-styled.  Illegitimate  }•  16  0 

union     .    .  


Mid-styled  form,  by  pollen  of  longest  sta- 
mens of  short-styled.  Illegitimate 
union 


10 


172    HETEROSTYLED  TEIMORPHIC  PLANTS.    CHAP.  TV. 


TABLE  27 — continued. 
Oxalis  Valdiviana  (from  Hildebrand). 


Number 

Number 

Number 

Nature  of  Union. 

Flowers 
fertilised. 

of 
Capsules 
produced. 

of 
Seeds  per 
Cap.uL 

Short-styled  form,  by  pollen  of  shortest] 
stamens  of  long  -  styled.      Legitimate  > 

18 

18 

11.0 

union      J 

Short-styled  form,  by  pollen  of  shortest] 
stamens   of   mid  -  styled.      Legitimate  > 

10 

10 

11.3 

union     J 

Short-styled  form,  by  pollen  of  own  and  ] 
own-form  longest  stamens.   Illegitimate  > 

21 

0 

0 

Short-styled  form,  by  pollen  of  own  and] 

own-form  mid-length  stamens.    Illegiti-  > 

22 

0 

0 

mate  union     J 

Short-styled  form,  by  pollen  of  longest] 
stamens  of  mid  -  styled.     Illegitimate  > 

4 

0 

0 

union     J 

Short-styled  form,  by  pollen  of  mid-length  ] 
stamens    of   long-styled.      Illegitimate  >• 
union  .              .  j 

3 

0 

0 

We  here  have  the  remarkable  result  that  every  one 
of  138  legitimately  fertilised  flowers  on  the  three  forms 
yielded  capsules  containing  on  an  average  11.33  seeds. 
Whilst  of  the  255  illegitimately  fertilised  flowers,  only 
6  yielded  capsules  which  contained  3.83  seeds  on  an 
average.  Therefore  the  fertility  of  the  six  legitimate 
to  that  of  the  twelve  illegitimate  unions,  as  judged 
by  the  proportion  of  flowers  that  yielded  capsules,  is 
as  100  to  2,  and  as  judged  by  the  average  number  of 
seeds  per  capsule  as  100  to  34.  It  may  be  added  that 
some  plants  which  were  protected  by  nets  did  not  spon- 
taneously produce  any  fruit;  nor  did  one  which  was 
left  uncovered  by  itself  and  was  visited  by  bees.  On 
the  other  hand,  scarcely  a  single  flower  on  some  uncov- 


CHAP.  IV.  OXALIS  EEGNELLI.  173 

ered  plants  of  the  three  forms  growing  near  together 
failed  to  produce  fruit. 

Oxalis  Regnelli. — This  species  bears  white  flowers 
and  inhabits  Southern  Brazil.  Hildebrand  says  that 
the  stigma  of  the  long-styled  form  is  somewhat  larger 
than  that  of  the  mid-styled  and  this  than  that  of  the 
short-styled.  The  pistil  of  the  latter  is  clothed  with  a 
few  hairs,  whilst  it  is  very  hairy  in  the  other  two 
forms.  The  diameter  of  the  pollen-grains  from  both 
sets  of  the  longest  stamens  equals  9  divisions  of  the 
micrometer, — that  from  the  mid-length  stamens  of  the 
long-styled  form  between  8  and  9,  and  of  the  short- 
styled  8, — and  that  from  the  shortest  stamens  of  both 
sets  7.  So  that  the  extreme  difference  in  diameter  is 
as  9  to  7,  or  as  100  to  78.  The  experiments  made  by 
Hildebrand,  which  are  not  so  numerous  as  in  the  last 
case,  are  given  in  Table  28  in  the  same  manner  as 
before. 

The  results  are  nearly  the  same  as  in  the  last  case, 
but  more  striking;  for  41  flowers  belonging  to  the 
three  forms  fertilised  legitimately  all  yielded  capsules, 
containing  on  an  average  10.31  seeds;  whilst  39 
flowers  fertilised  illegitimately  did  not  yield  a  single 
capsule  or  seed.  Therefore  the  fertility  of  the  six 
legitimate  to  that  of  the  several  illegitimate  unions, 
as  judged  both  by  the  proportion  of  flowers  which 
yielded  capsules  and  by  the  average  number  of  con- 
tained seeds,  is  as  100  to  0. 

Oxalis  speciosa. — This  species,  which  bears  pink 
flowers,  was  introduced  from  the  Cape  of  Good  Hope. 
A  sketch  of  the  reproductive  organs  of  the  three 
forms  (Fig.  11)  has  already  been  given.  The  stigma 
of  the  long-styled  form  (with  the  papilla  on  its  sur- 
face included)  is  twice  as  large  as  that  of  the  short- 
styled,  and  that  of  the  mid-styled  intermediate  in  size. 


174    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 


TABLE  28. 
Oxalis  JRegnelli  (from  Hildebrand). 


Number 

Number 

Aver 

N»ture  of  Union. 

Flowers 
fertilised. 

of 
Capsules 
proceed. 

Numbefof 
S.>eds  per 
C»psule. 

Long-styled  form,  by  pollen  of  longest  sta-  1 
mens  of  short-styled.   Legitimate  union  j 

6 

6 

10.1 

Long-styled  form,  by  pollen  of  longest  sta-  I 
mens  of  mid-styled.    Legitimate  union,  j 

5 

5 

10.6 

Long-styled  form,  by  pollen  of  own  mid-  } 
length  stamens.    Illegitimate  union      .  j 

4 

0 

0 

Long-styled  form,  by  pollen  of  own  short-  ) 
est  stamen.     Illegitimate  union    .     .    .  j 

1 

0 

0 

Mid-styled  form,  by  pollen  of  mid-length  ] 

stamens    of  short-styled.      Legitimate  > 

9 

9 

10.4 

union     J 

Mid-styled  form,  by  pollen  of  mid-length  ] 

stamens    of    long-styled.      Legitimate  > 

10 

10 

10.1 

Mid-styled  form,  by  pollen  of  own  longest  ) 

stamens.     Illegitimate  union    .     .     .     .  J 

Mid-styled  form,  by  pollen  of  own  shortest  I 
stamens.     Illegitimate  union   .     .     .     .  j 

2 

0 

0 

Mid-styled  form,  by  pollen  of  longest  sta-  ) 
mens  of  short-styled.  Illegitimate  union  j 

1 

0 

0 

Short-styled  form,  by  pollen  of  shortest] 
stamens    of  mid  -  styled.      Legitimate  > 

9 

9 

10.6 

Short-styled  form,  by  pollen  of  shortest] 
stamens  of  long  -  styled.      Legitimate  > 

2 

2 

9.5 

Short-styled  form,  by  pollen  of  own  mid-  ) 
length  stamens.     Illegitimate  union      .  j 

12 

0 

0 

Short-styled  form,  by  pollen  of  own  long-  1 
est  stamens.     Illegitimate  union  .     .     .  J 

9 

0 

0 

Short-styled  form,  by  pollen  of  mid-length  ] 
stamens   of   long-styled.      Illegitimate  > 

1 

0 

0 

CHAP.  IV. 


OXALIS  SPECIOSA. 


175 


The  pollen-grains  from  the  stamens  in  the  three  forms 
are  in  their  longer  diameters  as  follows : — 


Divisions  of  the 


From  the  longest  stamens  of  short-styled   . 
"       mid-length     " 
"      longest  stamens  of  mid-styled    . 
"       shortest  "  ,  . 

"       mid-length  stamens  of  long-styled 
"       shortest          "  " 


15  to  16 
12  "  13 

16 
11  to  12 

14 

12 


Therefore  the  extreme  difference  in  diameter  is  as 
16  to  11,  or  as  100  to  69;  but  as  the  measurements 
were  taken  at  different  times,  they  are  probably  only 
approximately  accurate.  The  results  of  my  experiments 
in  fertilising  the  three  forms  are  given  in  the  following 
table. 

TABLE  29. 
Oxalis  speciosa. 


Number 

Nnmber 

Average 

Nature  of  Union. 

of 

of 

Number  of 

fertilised. 

produced. 

CapX 

Long-styled  form,   by  pollen  of  longest  ) 
stamens    of  short-styled.      Legitimate  > 

19 

15 

57.4 

union     J 

Long-styled  form,   by  pollen  of  longest) 
stamens    of    mid-styled.       Legitimate  > 

4 

3 

59.0 

union     J 

Long-styled  form,  by  pollen  of  own-form  ) 
mid-length  stamens.  Illegitimate  union  ) 

9 

2 

42.5 

Long-styled  form,  by  pollen  of  own-form  I 
shortest  stamens.    Illegitimate  union  .  j 

11 

0 

0 

Long-styled  form,  by  pollen  of  shortest) 

stamens    of  mid-styled.       Illegitimate  > 

4 

0 

0 

union      .  J 

Long-styled  form,  by  pollen  of  mid-length  ~) 
stamens  of  short-styled.      Illegitimate  > 

12 

5 

30.0 

union      J 

176    HETEROSTYLED  TRIMORPH1C  PLANTS.    CHAP.  IV. 


TABLE  29 — continued. 
Oxalis  speciosa. 


Nature  of  Union. 

Number 

JEss. 

Number 
of 
Capsules 
produced. 

Average 
Number  of 
Seeds  per 
CapsuTo. 

Mid-styled  form,  by  pollen  of  mid-length  ) 
stamens  of  long-styled.  Legitimate  > 

3 

3 

63.6 

Mid-styled  form,  by  pollen  of  mid-length  ) 
stamens  of  short-styled.  Legitimate  > 
union  J 

4 

4 

56.3 

Mid-styled  form,  by  mixed  pollen  from] 
both  own-form  longest  and  shortest  sta-  > 
mens.  Illegitimate  union  j 

9 

2 

19 

Mid-styled  form,  by  pollen  of  longest) 
stamens  of  short-styled.  Illegitimate  > 

12 

1 

8 

Short-styled  form,  by  pollen  of  shortest) 
stamens  of  mid-styled.  Legitimate  >• 

3 

2 

67 

Short-styled  form,  by  pollen  of  shortest) 
stamens  of  long-styled.  Legitimate  > 
union  J 

3 

3 

54.3 

Short-styled  form,  by  pollen  of  own-form  ) 
longest  stamens.  Illegitimate  union  .  J 

5 

1 

8 

Short-styled  form,  by  pollen  of  own-form  I 
mid-length  stamens.  Illegitimate  union  j 

3 

0 

0 

Short-styled  form,  by  both  pollens  mixed  ) 
together,  of  own-form  longest  and  mid-  > 
length  stamens.  Illegitimate  union  .  J 

13 

0 

0 

Short-styled  form,  by  pollen  of  longest) 
stamens  of  mid-styled.  Illegitimate  > 

7 

0 

0 

Short-styled  form,  by  pollen  of  mid-length  ) 
stamens  of  long-styled.  Illegitimate  > 
union  J 

10 

1 

54 

We  here  see  that  thirty-six  flowers  on  the  three 
forms  legitimately  fertilised  yielded  30  capsules,  these 
containing  on  an  average  58.36  seeds.  Ninety-five 


CHAP.  IV.  OXALIS  ROSEA.  177 

flowers  illegitimately  fertilised  yielded  12  capsules, 
containing  on  an  average  28.58  seeds.  Therefore  the 
fertility  of  the  six  legitimate  to  that  of  the  twelve 
illegitimate  unions,  as  judged  by  the  proportion  of 
flowers  which  yielded  capsules,  is  as  100  to  15,  and 
judged  by  the  average  number  of  seeds  per  capsule,  as 
100  to  49.  This  plant,  in  comparison  with  the  two 
South  American  species  previously  described,  produces 
many  more  seeds,  and  the  illegitimately  fertilised  flow- 
ers are  not  quite  so  sterile. 

Oxalis  rosea. — Hildebrand  possessed  in  a  living  state 
only  the  long-styled  form  of  this  trimorphic  Chilian 
species.*  The  pollen-grains  from  the  two  sets  of 
anthers  differ  in  diameter  as  9  to  7.5,  or  as  100  to  83. 
He  has  further  shown  that  there  is  an  analogous  dif- 
ference between  the  grains  from  the  two  sets  of  an- 
thers of  the  same  flower  in  five  other  species  of  Oxalis, 
besides  those  already  described.  The  present  species 
differs  remarkably  from  the  long-styled  form  of  the 
three  species  previously  experimented  on,  in  a  much 
larger  proportion  of  the  flowers  setting  capsules  when 
fertilised  with  their  own-form  pollen.  Hildebrand  fer- 
tilised 60  flowers  with  pollen  from  the  mid-length 
stamens  (of  either  the  same  or  another  flower),  and 
they  yielded  no  less  than  55  capsules,  or  92  per  cent. 
These  capsules  contained  on  an  average  5.62  seeds; 
but  we  have  no  means  of  judging  how  near  an  approach 
this  average  makes  to  that  from  flowers  legitimately 
fertilised.  He  also  fertilised  45  flowers  with  pollen 
from  the  shortest  stamens,  and  these  yielded  only  17 
capsules,  or  31  per  cent.,  containing  on  an  average 
only  2.65  seeds.  We  thus  see  that  about  thrice  as 
many  flowers,  when  fertilised  with  pollen  from  the 


*  '  Monatsber.  der  Akad.  der  Wiss.  Berlin,'  1866,  p.  372. 


178    HETEROSTYLED  TEIMORPHIC  PLANTS.    CHAP.  IV. 

mid-length  stamens,  produced  capsules,  and  these 
contained  twice  as  many  seeds  as  did  the  flowers 
fertilised  with  pollen  from  the  shortest  stamens. 
It  thus  appears  (and  we  find  some  evidence  of 
the  same  fact  with  0.  speciosa)  that  the  same  rule 
holds  good  with  Oxalis  as  with  Lythrum  salicaria; 
namely,  that  in  any  two  unions,  the  greater  the  in- 
equality in  length  between  the  pistils  and  stamens,  or, 
which  is  the  same  thing,  the  greater  the  distance  of 
the  stigma  from  the  anthers,  the  pollen  of  which  is 
used  for  fertilisation,  the  less  fertile  is  the  union, — 
whether  judged  by  the  proportion  of  flowers  which 
set  capsules,  or  by  the  average  number  of  seeds  per 
capsule.  The  rule  cannot  be  explained  in  this  case 
any  more  than  in  that  of  Lythrum,  by  supposing  that 
wherever  there  is  greater  liability  to  self-fertilisation, 
this  is  checked  by  the  union  being  rendered  more  ster- 
ile; for  exactly  the  reverse  occurs,  the  liability  to  self- 
fertilisation  being  greatest  in  the  unions  between  the 
pistils  and  stamens  which  approach  each  other  the 
nearest,  and  these  are  the  more  fertile.  I  may  add  that 
I  also  possessed  some  long-styled  plants  of  this  species : 
one  was  covered  by  a  net,  and  it  set  spontaneously  a 
few  capsules,  though  extremely  few  compared  with  those 
produced  by  a  plant  growing  by  itself,  but  exposed  to 
the  visits  of  bees. 

With  most  of  the  species  of  Oxalis  the  short-styled 
form  seems  to  be  the  most  sterile  of  the  three  forms, 
when  these  are  illegitimately  fertilised;  and  I  will  add 
two  other  cases  to  those  already  given.  I  fertilised 
29  short-styled  flowers  of  0.  compressa  with  pollen  from 
their  own  two  sets  of  stamens  (the  pollen-grains  of 
which  differ  in  diameter  as  100  to  83),  and  not  one 
produced  a  capsule.  I  formerly  cultivated  during 
several  years  the  short-styled  form  of  a  species  pur- 


CHAP.  IV.         OXALIS,  OTHER  SPECIES  OF.  179 

chased  under  the  name  of  0.  Bowii  (but  I  have  some 
doubts  whether  it  was  rightly  named),  and  fertilised 
many  flowers  with  their  own  two  kinds  of  pollen, 
which  differ  in  diameter  in  the  usual  manner,  but 
never  got  a  single  seed.  On  the  other  hand,  Hil- 
debrand  says  that  the  short-styled  form  of  0.  Deppei, 
growing  by  itself,  yields  plenty  of  seed;  but  it  is  not 
positively  known  that  this  species  is  heterostyled;  and 
the  pollen-grains  from  the  two  sets  of  anthers  do  not 
differ  in  diameter. 

Some  facts  communicated  to  me  by  Fritz  Miiller 
afford  excellent  evidence  of  the  utter  sterility  of  one 
of  the  forms  of  certain  trimorphic  species  of  Oxalis, 
when  growing  isolated.  He  has  seen  in  St.  Catharina, 
in  Brazil,  a  large  field  of  young  sugar-cane,  many 
acres  in  extent,  covered  with  the  red  blossoms  of  one 
form  alone,  and  these  did  not  produce  a  single  seed. 
His  own  land  is  covered  with  the  short-styled  form  of 
a  white-flowered  trimorphic  species,  and  this  is  equally 
sterile;  but  when  the  three  forms  were  planted  near 
together  in  his  garden,  they  seeded  freely.  With  two 
other  trimorphic  species  he  finds  that  isolated  plants 
are  always  sterile. 

Fritz  Miiller  formerly  believed  that  a  species  of 
Oxalis,  which  is  so  abundant  in  St.  Catharina  that  it 
borders  the  roads  for  miles,  was  dimorphic  instead  of 
trimorphic.  Although  the  pistils  and  stamens  vary 
greatly  in  length,  as  was  evident  in  some  specimens 
sent  to  me,  yet  the  plants  can  be  divided  into  two 
sets,  according  to  the  lengths  of  these  organs.  A 
large  proportion  of  the  anthers  are  of  a  white  colour 
and  quite  destitute  of  pollen;  others  which  are  pale 
yellow  contain  many  bad  with  some  good  grains;  and 
others  again  which  are  bright  yellow  have  apparently 
sound  pollen;  but  he  has  never  succeeded  in  finding 


180    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

any  fruit  on  this  species.  The  stamens  in  some  of 
the  flowers  are  partially  converted  into  petals.  Fritz 
Miiller,  after  reading  my  description,  hereafter  to  be 
given,  of  the  illegitimate  offspring  of  various  hetero- 
styled  species,  suspects  that  these  plants  of  Oxalis 
may  be  the  variable  and  sterile  offspring  of  a  single 
form  of  some  trimorphic  species,  perhaps  accidentally 
introduced  into  the  district,  which  has  since  been 
propagated  asexually.  It  is  probable  that  this  kind 
of  propagation  would  be  much  aided  by  there  being 
no  expenditure  in  the  production  of  seed. 

Oxalis  (Biophytum)  sensitiva. — This. plant  is  ranked 
by  many  botanists  as  a  distinct  genus.  Mr.  Thwaites 
sent  me  a  number  of  flowers  preserved  in  spirits  from 
Ceylon,  and  they  are  clearly  trimorphic.  The  style 
of  the  long-styled  form  is  clothed  with  many  scattered 
hairs,  both  simple  and  glandular;  such  hairs  are  much 
fewer  on  the  style  of  the  mid-styled,  and  quite  ab- 
sent from  that  of  the  short-styled  form;  so  that  this 
plant  resembles  in  this  respect  0.  Valdiviana  and 
Regnelli.  Calling  the  length  of  the  two  lobes  of 
the  stigma  of  the  long-styled  form  100,  that  of  the 
mid-styled  is  141,  and  that  of  the  short-styled  164. 
In  all  other  cases  in  which  the  stigma  in  this  genus 
differs  in  size  in  the  three  forms,  the  difference  is  of 
a  reversed  nature,  the  stigma  of  the  long-styled  being 
the  largest,  and  that  of  the  short-styled  the  smallest. 
The  diameter  of  the  pollen-grains  from  the  longest 
stamens  being  represented  by  100,  those  from  the  mid- 
length  stamens  are  91,  and  those  from  the  shortest 
stamens  84  in  diameter.  This  plant  is  remarkable,  as 
we  shall  see  in  the  last  chapter  of  this  volume,  by  pro- 
ducing long-styled,  mid-styled,  and  short-styled  cleisto- 
gamic  flowers. 


CHAP.  IV.       OXALIS,  HOMOSTYLED  SPECIES.  181 

Homostyled  Species  of  Oxalis. — Although  the  ma- 
jority of  the  species  in  the  large  genus  Oxalis  seem  to 
be  trimorphic,  some  are  homostyled,  that  is,  exist  under 
a  single  form;  for  instance,  the  common  0.  aceto- 
sella,  and  according  to  Hildebrand  two  other  widely 
distributed  European  species,  0.  stricta  and  corniculata. 
Fritz  Miiller  also  informs  me  that  a  similarly  consti- 
tuted species  is  found  in  St.  Catharina,  and  that  it  ia 
quite  fertile  with  its  own  pollen  when  insects  are  ex- 
cluded. The  stigmas  of  0.  stricta  and  of  another  homo- 
styled  species,  viz.  0.  tropceoloides,  commonly  stand  on 
a  level  with  the  upper  anthers,  and  both  these  species 
are  likewise  quite  fertile  when  insects  are  excluded. 

With  respect  to  0.  acetosella,  Hildebrand  says  that 
in  all  the  many  specimens  examined  by  him  the  pistil 
exceeded  the  longer  stamens  in  length.  I  procured 
108  flowers  from  the  same  number  of  plants  growing  in 
three  distant  parts  of  England;  of  these  86  had  their 
stigmas  projecting  considerably  above,  whilst  22  had 
them  nearly  on  a  level  with  the  upper  anthers.  In 
one  lot  of  17  flowers  from  the  same  wood,  the  stigmas  in 
every  flower  projected  fully  as  much  above  the  upper 
anthers  as  these  stood  above  the  lower  anthers.  So 
that  these  plants  might  fairly  be  compared  with  the 
long-styled  form  of  a  heterostyled  species;  and  I  at 
first  thought  that  0.  acetosella  was  trimorphic.  But 
the  case  is  one  merely  of  great  variability.  The 
pollen-grains  from  the  two  sets  of  anthers,  as  observed 
by  Hildebrand  and  myself,  do  not  differ  in  diameter. 
I  fertilised  twelve  flowers  on  several  plants  with  pol- 
len from  a  distinct  plant,  choosing  those  with  pistils 
of  a  different  length;  and  10  of  these  (i.  e.  83  per  cent.) 
produced  capsules,  which  contained  on  an  average  7.9 
seeds.  Fourteen  flowers  were  fertilised  with  their  own 
pollen,  and  11  of  these  (i.  e.  79  per  cent.)  yielded  cap- 


182    HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

sules,  containing  a  larger  average  of  seed,  namely,  9.2. 
These  plants,  therefore,  in  function  show  not  the 
least  sign  of  being  heterostyled.  I  may  add  that  18 
flowers  protected  by  a  net  were  left  to  fertilise  them- 
selves, and  only  10  of  these  (i.  e.  55  per  cent.)  yielded 
capsules,  which  contained  on  an  average  only  6.3  seeds. 
So  that  the  access  of  insects,  or  artificial  aid  in  plac- 
ing pollen  on  the  stigma,  increases  the  fertility  of  the 
flowers;  and  I  found  that  this  applied  especially  to 
those  having  shorter  pistils.  It  should  be  remem- 
bered that  the  flowers  hang  downwards,  so  that  those 
with  short  pistils  would  be  the  least  likely  to  receive 
their  own  pollen,  unless  they  were  aided  in  some 
manner. 

Finally,  as  Hildebrand  has  remarked,  there  is  no 
evidence  that  any  of  the  heterostyled  species  of  Oxalis 
are  tending  towards  a  dioecious  condition,  as  Zuccarini 
and  Lindley  inferred  from  the  differences  in  the  re- 
productive organs  of  the  three  forms,  the  meaning  of 
which  they  did  not  understand. 

PONTEDEKIA    [SP.  ?]     (PONTEDERIACE^) . 

Fritz  Miiller  found  this  aquatic  plant,  which  is  al- 
lied to  the  Liliaceae,  growing  in  the  greatest  profusion 
on  the  banks  of  a  river  in  Southern  Brazil.*  But  only 
two  forms  were  found,  the  flowers  of  which  include 
three  long  and  three  short  stamens.  The  pistil  of  the 
long-styled  form,  in  two  dried  flowers  which  were  sent 
me,  was  in  length  as  100  to  32,  and  its  stigma  as  100 
to  80,  compared  with  the  same  organs  in  the  short- 
styled  form.  The  long-styled  stigma  projects  consid- 
erably above  the  upper  anthers  of  the  same  flower,  and 


*  "Ueberden  Trimorphisirms  der  Pontcderien,"  'Jenaische  Zeit- 
schrift,'  &c.,  Band  6,  1871,  p.  74. 


CHAP.  IV.  PONTEDERIA.  183 

stands  on  a  level  with  the  upper  ones  of  the  short-styled 
form.  In  the  latter  the  stigma  is  seated  beneath  both 
its  own  sets  of  anthers,  and  is  on  a  level  with  the  an- 
thers of  the  shorter  stamens  in  the  long-styled  form. 
The  anthers  of  the  longer  stamens  of  the  short-styled 
form  are  to  those  of  the  shorter  stamens  of  the  long- 
styled  form  as  100  to  88  in  length.  The  pollen-grains 
distended  with  water  from  the  longer  stamens  of  the 
short-styled  form  are  to  those  from  the  shorter  stamens 
of  the  same  form  as  100  to  87  in  diameter,  as  deduced 
from  ten  measurements  of  each  kind.  We  thus  see  that 
the  organs  in  these  two  forms  differ  from  one  another 
and  are  arranged  in  an  analogous  manner,  as  in  the 
long-  and  short-styled  forms  of  the  trimorphic  species 
of  Lythrum  and  Oxalis.  Moreover  the  longer  stamens 
of  the  long-styled  form  of  Pontederia,  and  the  shorter 
ones  of  the  short-styled  form,  are  placed  in  a  proper 
position  for  fertilising  the  stigma  of  a  mid-styled  form. 
But  Fritz  Miiller,  although  he  examined  a  vast  number 
of  plants,  could  never  find  one  belonging  to  the  mid- 
styled  form.  The  older  flowers  of  the  long-styled 
and  short-styled  plants  had  set  plenty  of  apparently 
good  fruit;  and  this  might  have  been  expected,  as 
they  could  legitimately  fertilise  one  another.  Al- 
though he  could  not  find  the  mid-styled  form  of 
this  species,  he  possessed  plants  of  another  species 
growing  in  his  garden,  and  all  these  were  mid-styled; 
and  in  this  case  the  pollen-grains  from  the  anthers  of 
the  longer  stamens  were  to  those  from  the  shorter  sta- 
mens of  the  same  flower  as  100  to  86  in  diameter,  as 
deduced  from  ten  measurements  of  each  kind.  These 
mid-styled  plants  growing  by  themselves  never  pro- 
duced a  single  fruit. 

Considering  these  several  facts,  there  can  hardly 
be  a  doubt  that  both  these  species  of  Pontederia  are 


184:   HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

heterostyled  and  trimorphic.  This  case  is  an  interest- 
ing one,  for  no  other  Monocotyledonous  plant  is  known 
to  be  heterostyled.  Moreover  the  flowers  are  irregular, 
and  all  other  heterostyled  plants  have  almost  sym- 
metrical flowers.  The  two  forms  differ  somewhat  in 
the  colour  of  their  corollas,  that  of  the  short-styled 
being  of  a  darker  blue,  whilst  that  of  the  long-styled 
tends  towards  violet,  and  no  other  such  case  is  known. 
Lastly,  the  three  longer  stamens  alternate  with  the 
three  shorter  ones,  whereas  in  Lythrum  and  Oxalis 
the  long  and  short  stamens  belong  to  distinct  whorls. 
With  respect  to  the  absence  of  the  mid-styled  form  in 
the  case  of  the  Pontederia  which  grows  wild  in  Southern 
Brazil,  this  would  probably  follow  if  only  two  forms 
had  been  originally  introduced  there;  for,  as  we  shall 
hereafter  see  from  the  observations  of  Hildebrand, 
Fritz  Miiller,  and  myself,  when  one  form  of  Oxalis  is 
fertilised  exclusively  by  either  of  the  other  two  forms 
the  offspring  generally  belong  to  the  two  parent- 
forms. 

Fritz  Miiller  has  recently  discovered,  as  he  informs 
me,  a  third  species  of  Pontederia,  with  all  three  forms 
growing  together  in  pools  in  the  interior  of  S.  Brazil; 
so  that  no  shadow  of  doubt  can  any  longer  remain 
about  this  genus  including  trimorphic  species.  He 
sent  me  dried  flowers  of  all  three  forms.  In  the  long- 
styled  form  the  stigma  stands  a  little  above  the  tips 
of  the  petals,  and  on  a  level  with  the  anthers  of  the 
longest  stamens  in  the  other  two  forms.  The  pistil  is 
in  length  to  that  of  the  mid-styled  as  100  to  56,  and 
to  that  of  the  short-styled  as  100  to  16.  Its  summit  is 
rectangularly  bent  upwards,  and  the  stigma  is  rather 
broader  than  that  of  the  mid-styled,  and  broader  in 
about  the  ratio  of  7  to  4  than  that  of  the  short-styled. 
In  the  mid-styled  form,  the  stigma  is  placed  rather 


CHAP.  IV.  PONTEDEEIA.  185 

above  the  middle  of  the  corolla,  and  nearly  on  a  level 
with  the  mid-length  stamens  in  the  other  two  forms: 
its  summit  is  a  little  bent  upwards.  In  the  short- 
styled  form  the  pistil  is,  as  we  have  seen,  very  short, 
and  differs  from  that  in  the  other  two  forms  in  being 
straight.  It  stands  rather  beneath  the  level  of  the 
anthers  of  the  shortest  stamens  in  the  long-styled  and 
mid-styled  forms.  The  three  anthers  of  each  set  of 
stamens,  more  especially  those  of  the  shortest  stamens, 
are  placed  one  beneath  the  other,  and  the  ends  of  the 
filaments  are  bowed  a  little  upwards,  so  that  the  pollen 
from  all  the  anthers  would  be  effectively  brushed  off 
by  the  proboscis  of  a  visiting  insect.  The  relative 
diameters  of  the  pollen-grains,  after  having  been  long 
soaked  in  water,  are  given  in  the  following  list,  as 
measured  by  my  son  Francis : — 


Long-styled  form,  from  the  mid-length  stamens    .     .    13.2 

(Average  of  20  measurements.) 
"  "        from  the  shortest  stamens    ...      9.0 

(10  measurements.) 
Mid-styled  form,  from  the  longest  stamens    ....    16.4 

(15  measurements.) 
"  "        from  the  shortest  stamens     ...      9.1 

(20  measurements.) 
Short-styled  form,  from  the  longest  stamens ....    14.6 

(20  measurements. ) 

"  "        from  the  mid-length  stamens    .     .    12.3 

(20  measurements.) 

We  have  here  the  usual  rule  of  the  grains  from  the 
longer  stamens,  the  tubes  of  which  have  to  penetrate 
the  longer  pistil,  being  larger  than  those  from  the 
stamens  of  less  length.  The  extreme  difference  in 
diameter  between  the  grains  from  the  longest  stamens 
of  the  mid-styled  form,  and  from  the  shortest  stamens 
of  the  long-styled,  is  as  16.4  to  9.0,  or  as  100  to  55; 
14 


186   HETEROSTYLED  TRIMORPHIC  PLANTS.    CHAP.  IV. 

and  this  is  the  greatest  difference  observed  by  me  in 
any  heterostyled  plant.  It  is  a  singular  fact  that  the 
grains  from  the  corresponding  longest  stamens  in  the 
two  forms  differ  considerably  in  diameter;  as  do  those 
in  a  lesser  degree  from  the  corresponding  mid-length 
stamens  in  the  two  forms;  whilst  those  from  the  cor- 
responding shortest  stamens  in  the  long-  and  mid- 
styled  forms  are  almost  exactly  equal.  Their  in- 
equality in  the  two  first  cases  depends  on  the  grains 
in  both  sets  of  anthers  in  the  short-styled  form  being 
smaller  than  those  from  the  corresponding  anthers  in 
the  other  two  forms;  and  here  we  hve  a  case  parallel 
with  that  of  the  mid-styled  form  of  Lytlirum  salicaria. 
In  this  latter  plant  the  pollen-grains  of  the  mid-styled 
forms  are  of  smaller  size  and  have  less  fertilising  power 
than  the  corresponding  ones  in  the  other  two  forms; 
whilst  the  ovarium,  however  fertilised,  yields  a  greater 
number  of  seeds;  so  that  the  mid-styled  form  is  alto- 
gether more  feminine  in  nature  than  the  other  two 
forms.  In  the  case  of  Pontederia,  the  ovarium  in- 
cludes only  a  single  ovule,  and  what  the  meaning  of 
the  difference  in  size  between  the  pollen-grains  from 
the  corresponding  sets  of  anthers  may  be,  I  will  not  pre- 
tend to  conjecture. 

The  clear  evidence  that  the  species  just  described  is 
heterostyled  and  trimorphic  is  the  more  valuable  as 
there  is  some  doubt  with  respect  to  P.  cordata,  an  in- 
habitant of  the  United  States.  Mr.  Leggett  suspects  * 
that  it  is  either  dimorphic  or  trimorphic,  for  the 
pollen-grains  of  the  longer  stamens  are  "  more  than 
twice  the  diameter  or  than  eight  times  the  mass  of 
the  grains  of  the  shorter  stamens.  Though  minute, 
these  smaller  grains  seem  as  perfect  as  the  larger 


*  '  Bull,  of  the  Torrey  Botanical  Club,'  1875,  vol.  vi.  p.  62. 


CHAP.  IV.  PONTEDERIA.  187 

ones."  On  the  other  hand,  he  says  that  in  all  the 
mature  flowers,  "  the  style  was  as  long  at  least  as 
the  longer  stamens ; "  "  whilst  in  the  young  flowers  it 
was  intermediate  in  length  between  the  two  sets  of  sta- 
mens;" and  if  this  be  so,  the  species  can  hardly  be 
heterostyled. 


188  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 


CHAPTER  V. 
ILLEGITIMATE  OFFSPEINQ  OF  HETEKOSTYLED  PLANTS. 

Illegitimate  offspring  from  all  three  forms  of  Lythrum  salicaria — Their 
dwarfed  stature  and  sterility,  some  utterly  barren,  some  fertile — 
Oxalis,  transmission  of  form  to  the  legitimate  and  illegitimate 
seedlings — Primula  Sinensis,  illegitimate  offspring  in  some  degree 
dwarfed  and  infertile — Equal-styled  varieties  of  P.  Sinensis,  auri- 
cula, farinosa,  and  elatior — P.  vulgaris,  red-flowered  variety,  illegi- 
timate seedlings  sterile — P.  veris,  illegitimate  plants  raised  during 
several  successive  generations,  their  dwarfed  stature  and  sterility — 
Equal-styled  varieties  of  P.  veris — Transmission  of  form  by  Pul- 
monaria  and  Polygonum — Concluding  remarks — Close  parallelism 
between  illegitimate  fertilisation  and  hybridism. 

WE  have  hitherto  treated  of  the  fertility  of  the  flow- 
ers of  heterostyled  plants,  when  legitimately  and  illegiti- 
mately fertilised.  The  present  chapter  will  be  devoted 
to  the  character  of  their  offspring  or  seedlings.  Those 
raised  from  legitimately  fertilised  seeds  will  be  here 
called  legitimate  seedlings  or  plants,  and  those  from 
illegitimately  fertilised  seeds,  illegitimate  seedlings  or 
plants.  They  differ  chiefly  in  their  degree  of  fertility, 
and  in  their  powers  of  growth  or  vigour.  I  will  begin 
with  trimorphic  plants,  and  I  must  remind  the  reader 
that  each  of  the  three  forms  can  be  fertilised  in  six 
different  ways;  so  that  all  three  together  can  be  fer- 
tilised in  eighteen  different  ways.  For  instance,  a 
long-styled  form  can  be  fertilised  legitimately  by  the 
longest  stamens  of  the  mid-styled  and  short-styled 
forms,  and  illegitimately  by  its  own-form  mid-length 
and  shortest  stamens,  also  by  the  mid-length  stamens 
of  the  mid-styled  and  by  the  shortest  stamens  of  the 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     189 

short-styled  form;  so  that  the  long-styled  can  be  fer- 
tilised legitimately  in  two  ways  and  illegitimately  in 
four  ways.  The  same  holds  good  with  respect  to  the 
mid-styled  and  short-styled  forms.  Therefore  with 
trimorphic  species  six  of  the  eighteen  unions  yield 
legitimate  offspring,  and  twelve  yield  illegitimate  off- 
spring. 

I  will  give  the  results  of  my  experiments  in  detail, 
partly  because  the  observations  are  extremely  trouble- 
some, and  will  not  probably  soon  be  repeated — thus,  I 
was  compelled  to  count  under  the  microscope  above 
20,000  seeds  of  Lythrum  salicaria — but  chiefly  because 
light  is  thus  indirectly  thrown  on  the  important  sub- 
ject of  hybridism. 

LYTHRUM  SALICARIA. 

Of  the  twelve  illegitimate  unions  two  were  com- 
pletely barren,  so  that  no  seeds  were  obtained,  and  of 
course  no  seedlings  could  be  raised.  Seedlings  were, 
however,  raised  from  seven  of  the  ten  remaining 
illegitimate  unions.  Such  illegitimate  seedlings  when 
in  flower  were  generally  allowed  to  be  freely  and 
legitimately  fertilised,  through  the  agency  of  bees,  by 
other  illegitimate  plants  belonging  to  the  two  other 
forms  growing  close  by.  This  is  the  fairest  plan,  and 
was  usually  followed;  but  in  several  cases  (which 
will  always  be  stated)  illegitimate  plants  were  fer- 
tilised with  pollen  taken  from  legitimate  plants  be- 
longing to  the  other  two  forms;  and  this,  as  might 
have  been  expected,  increased  their  fertility.  Lythrum 
salicaria  is  much  affected  in  its  fertility  by  the  nature 
of  the  season;  and  to  avoid  error  from  this  source 
as  far  as  possible,  my  observations  were  continued 
during  several  years.  Some  few  experiments  were 


190  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

tried  in  1863.  The  summer  of  1864  was  too  hot  and 
dry,  and  though  the  plants  were  copiously  watered, 
some  few  apparently  suffered  in  their  fertility,  whilst 
others  were  not  in  the  least  affected.  The  years 
1865  and,  especially,  1866  were  highly  favourable. 
Only  a  few  observations  were  made  during  1867. 
The  results  are  arranged  in  classes  according  to  the 
parentage  of  the  plants.  In  each  case  the  average 
number  of  seeds  per  capsule  is  given,  generally  taken 
from  ten  capsules,  which,  according  to  my  experience, 
is  a  nearly  sufficient  number.  The  maximum  num- 
ber of  seeds  in  any  one  capsule  is  also  given;  and 
this  is  a  useful  point  of  comparison  with  the  nor- 
mal standard — that  is,  with  the  number  of  seeds  pro- 
duced by  legitimate  plants  legitimately  fertilised.  I 
will  give  likewise  in  each  case  the  minimum  number. 
When  the  maximum  and  minimum  differ  greatly,  if 
no  remark  is  made  on  the  subject,  it  may  be  under- 
stood that  the  extremes  are  so  closely  connected  by 
intermediate  figures  that  the  average  is  a  fair  one. 
Large  capsules  were  always  selected  for  counting,  in 
order  to  avoid  over-estimating  the  infertility  of  the  sev- 
eral illegitimate  plants. 

In  order  to  judge  of  the  degree  of  inferiority  in 
fertility  of  the  several  illegitimate  plants,  the  follow- 
ing statement  of  the  average  and  of  the  maximum 
number  of  seeds  produced  by  ordinary  or  legitimate 
plants,  when  legitimately  fertilised,  some  artificially 
and  some  naturally,  will  serve  as  a  standard  of  com- 
parison, and  may  in  each  case  be  referred  to.  But  I 
give  under  each  experiment  the  percentage  of  seeds 
produced  by  the  illegitimate  plants,  in  comparison 
with  the  standard  legitimate  number  of  the  same 
form.  For  instance,  ten  capsules  from  the  illegitimate 
long-styled  plant  (No.  10),  which  was  legitimately 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     191 

and  naturally  fertilised  by  other  illegitimate  plants, 
contained  on  an  average  44.2  seeds;  whereas  the 
capsules  on  legitimate  long-styled  plants,  legitimately 
and  naturally  fertilised  by  other  legitimate  plants,  con- 
tained on  an  average  93  seeds.  Therefore  this  illegiti- 
mate plant  yielded  only  47  per  cent,  of  the  full  and  nor- 
mal complement  of  seeds. 

Standard  Number  of  Seeds  produced  by  Legitimate 
Plants  of  the  three  Forms,  when  legitimately  fer- 
tilised. 

Long-styled  form:  average  number  of  seeds  in  each 
capsule,  93;  maximum  number  observed  out  of  twenty- 
three  capsules,  159. 

Mid-styled  form:  average  number  of  seeds,  130; 
maximum  number  observed  out  of  thirty-one  capsules, 
151. 

Short-styled  form:  average  number  of  seeds,  83.5; 
but  we  may,  for  the  sake  of  brevity,  say  83 ;  maximum 
number  observed  out  of  twenty-five  capsules,  112. 

CLASSES  I.  and  II.  Illegitimate  Plants  raised  from 
Long-styled  Parents  fertilised  with  pollen  from  the 
mid-length  or  the  shortest  stamens  of  other  plants  of 
the  same  form. 

From  this  union  I  raised  at  different  times  three 
lots  of  illegitimate  seedlings,  amounting  altogether  to 
56  plants.  I  must  premise  that,  from  not  foreseeing 
the  result,  I  did  not  keep  a  memorandum  whether  the 
eight  plants  of  the  first  lot  were  the  product  of  the 
mid-length  or  shortest  stamens  of  the  same  form;  but 
I  have  good  reason  to  believe  that  they  were  the  pro- 
duct of  the  latter.  These  eight  plants  were  much  more 
dwarfed,  and  much  more  sterile  than  those  in  the  other 


192  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

two  lots.  The  latter  were  raised  from  a  long-styled 
plant  growing  quite  isolated,  and  fertilised  by  the 
agency  of  bees  with  its  own  pollen:  and  it  is  almost 
certain,  from  the  relative  position  of  the  organs  of 
fructification,  that  the  stigma  under  these  circum- 
stances would  receive  pollen  from  the  mid-length 
stamens. 

All  the  fifty-six  plants  in  these  three  lots  proved 
long-styled;  now,  if  the  parent-plants  had  been  legiti- 
mately fertilised  by  pollen  from  the  longest  stamens  of 
the  mid-styled  and  short-styled  forms,  only  about  one- 
third  of  the  seedlings  would  have  been  long-styled, 
the  other  two-thirds  being  mid-styled  and  short-styled. 
In  some  other  trimorphic  and  dimorphic  genera  we 
shall  find  the  same  curious  fact,  namely,  that  the  long- 
styled  form,  fertilised  illegitimately  by  its  own-form 
pollen,  produces  almost  exclusively  long-styled  seed- 
lings.* 

The  eight  plants  of  the  first  lot  were  of  low  stature : 
three  which  I  measured  attained,  when  fully  grown,  the 
heights  of  only  28,  29,  and  47  inches ;  whilst  legitimate 
plants  growing  close  by  were  double  this  height,  one 
being  77  inches.  They  all  betrayed  in  their  general 
appearance  a  weak  constitution;  they  flowered  rather 
later  in  the  season,  and  at  a  later  age  than  ordinary 
plants.  Some  did  not  flower  every  year ;  and  one  plant, 
behaving  in  an  unprecedented  manner,  did  not  flower 
until  three  years  old.  In  the  two  other  lots  none  of 
the  plants  grew  quite  to  their  full  and  proper  height, 
as  could  at  once  be  seen  by  comparing  them  with  the 
adjoining  rows  of  legitimate  plants.  In  several  plants 
in  all  three  lots,  many  of  the  anthers  were  either 


*  Hildebrand  first  called  atten-  Primula  Rinensis :  but  his  results 
tion  ('Bot.  Zeitimg.'  Jan.  1,  1864,  were  not  nearly  so  uniform  as 
p.  5)  to  this  fact  in  the  case  of  mine. 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     193 

shrivelled  or  contained  brown  and  tough,  or  pulpy 
matter,  without  any  good  pollen-grains,  and  they  never 
shed  their  contents;  they  were  in  the  state  designated 
by  Gartner  *  as  contabescent,  which  term  I  will  for  the 
future  use.  In  one  flower  all  the  anthers  were  conta- 
bescent excepting .  two  which  appeared  to  the  naked 
eye  sound;  but  under  the  microscope  about  two-thirds 
of  the  pollen-grains  were  seen  to  be  small  and  shrivelled. 
In  another  plant,  in  which  all  the  anthers  appeared 
sound,  many  of  the  pollen-grains  were  shrivelled  and 
of  unequal  sizes.  I  counted  the  seeds  produced  by 
seven  plants  (1  to  7)  in  the  first  lot  of  eight  plants, 
probably  the  product  of  parents  fertilised  by  their  own- 
form  shortest  stamens,  and  the  seeds  produced  by  three 
plants  in  the  other  two  lots,  almost  certainly  the  pro- 
duct of  parents  fertilised  by  their  own-form  mid-length 
stamens. 

Plant   1.  This   long-styled  plant  was   allowed  during 

1863  to  be  freely  and  legitimately  fertilised  by  an  adjoining 
illegitimate  mid-styled  plant,  but  it  did  not  yield  a  single 
seed-capsule.    It  was  then  removed  and  planted  in  a  re- 
mote place  close  to  a  brother  long-styled  plant  No.  2,  so 
that  it  must  have  been  freely  though  illegitimately  fertil- 
ised; under  these  circumstances  it  did  not  yield  during 

1864  and  1865  a  single  capsule.    I  should  here  state  that  a 
legitimate  or  ordinary  long-styled  plant,  when  growing 
isolated,  and  freely  though  illegitimately  fertilised  by  in- 
sects with  its  own  pollen,  yielded  an  immense  number  of 
capsules,  which  contained  on  an  average  21.5  seeds. 

Plant  2.  This  long-styled  plant,  after  flowering  during 
1863  close  to  an  illegitimate  mid-styled  plant,  produced 
less  than  twenty  capsules,  which  contained  on  an  average 
between  four  and  five  seeds.  When  subsequently  growing 
in  company  with  Xo.  1,  by  which  it  will  have  been  illegit- 
imately fertilised,  it  yielded  in  1866  not  a  single  capsule, 
but  in  1865  it  yielded  twenty-two  capsules:  the  best  of 


*  'Beitriige  zur  Kenntniss  der  Befruchtung,'  1844,  p.  116. 


194  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

these,  fifteen  in  number,  were  examined;  eight  contained 
no  seed,  and  the  remaining  seven  contained  on  an  average 
only  three  seeds,  and  these  seeds  were  so  small  and  shriv- 
elled that  I  doubt  whether  they  would  have  germinated. 

Plants  3  and  4'  These  two  long-styled  plants,  after  be- 
ing freely  and  legitimately  fertilised  during  1863  by  the 
game  illegitimate  mid-styled  plant  as  in  the  last  case,  were 
as  miserably  sterile  as  No.  2. 

Plant  5.  This  long-styled  plant,  after  flowering  in  1863 
close  to  an  illegitimate  mid-styled  plant,  yielded  only  four 
capsules,  which  altogether  included  only  five  seeds.  Dur- 
ing 1864,  1865,  and  1866,  it  was  surrounded  either  by  ille- 
gitimate or  legitimate  plants  of  the  other  two  forms;  but 
it  did  not  yield  a  single  capsule.  It  was  a  superfluous  ex- 
periment, but  I  likewise  artificially  fertilised  in  a  legiti- 
mate manner  twelve  flowers;  but  not  one  of  these  pro- 
duced a  capsule;  so  that  this  plant  was  almost  absolutely 
barren. 

Plant  6.  This  long-styled  plant,  after  flowering  during 
the  favourable  year  of  1866,  surrounded  by  illegitimate 
plants  of  the  other  two  forms,  did  not  produce  a  single 
capsule. 

Plant  7.  This  long-styled  plant  was  the  most  fertile  of 
the  eight  plants  of  the  first  lot.  During  1865  it  was  sur- 
rounded by  illegitimate  plants  of  various  parentage,  many 
of  which  were  highly  fertile,  and  must  thus  have  been  legiti- 
mately fertilised.  It  produced  a  good  many  capsules,  ten 
of  which  yielded  an  average  of  36.1  seeds,  with  a  maximum 
of  47  and  a  minimum  of  22;  so  that  this  plant  produced 
39  per  cent,  of  the  full  number  of  seeds.  During  1864  it 
was  surrounded  by  legitimate  and  illegitimate  plants  of  the 
other  two  forms;  and  nine  capsules  (one  poor  one  being  re- 
jected) yielded  an  average  of  41.9  seeds,  with  a  maximum 
of  56  and  a  minimum  of  28 ;  so  that,  under  these  favourable 
circumstances,  this  plant,  the  most  fertile  of  the  first  lot, 
did  not  yield,  when  legitimately  fertilised,  quite  45  per 
cent,  of  the  full  complement  of  seeds. 

In  the  second  lot  of  plants  in  the  present  class  de- 
scended from  the  long-styled  form,  almost  certainly  fer- 
tilised with  pollen  from  its  own  mid-length  stamens, 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     195 

the  plants,  as  already  stated,  were  not  nearly  so  dwarfed 
or  so  sterile  as  in  the  first  lot.  All  produced  plenty  of 
capsules.  I  counted  the  number  of  seeds  in  only  three 
plants,  viz.  Nos.  8,  9,  and  10. 

Plant  8.  This  plant  was  allowed  to  be  freely  fertilised 
in  1864  by  legitimate  and  illegitimate  plants  of  the  other 
two  forms,  and  ten  capsules  yielded  on  an  average  41.1 
seeds,  with  a  maximum  of  73  and  a  minimum  of  11.  Hence 
this  plant  produced  only  44  per  cent,  of  the  full  comple- 
ment of  seeds. 

Plant  9,  This  long-styled  plant  was  allowed  in  1865  to 
be  freely  fertilised  by  illegitimate  plants  of  the  other  two 
forms,  most  of  which  were  moderately  fertile.  Fifteen 
capsules  yielded  on  an  average  57.1  seeds,  with  a  maximum 
of  86  and  a  minimum  of  23.  Hence  the  plant  yielded  68 
per  cent,  of  the  full  complement  of  seeds. 

Plant  10.  This  long-styled  plant  was  freely  fertilised 
at  the  same  time  and  in  the  same  manner  as  the  last.  Ten 
capsules  yielded  an  average  of  44.2  seeds,  with  a  maximum 
of  69  and  a  minimum  of  25.  Hence  this  plant  yielded  47 
per  cent,  of  the  full  complement  of  seeds. 

The  nineteen  long-styled  plants  of  the  third  lot,  of 
the  same  parentage  as  the  last  lot,  were  treated  dif- 
ferently; for  they  flowered  during  1867  by  themselves, 
so  that  they  must  have  been  illegitimately  fertilised 
by  one  another.  It  has  already  been  stated  that  a 
legitimate  long-styled  plant,  growing  by  itself  and 
visited  by  insects,  yielded  an  average  of  21.5  seeds 
per  capsule,  with  a  maximum  of  35;  but,  to  judge 
fairly  of  its  fertility,  it  ought  to  have  been  observed 
during  successive  seasons.  We  may  also  infer  from 
analogy  that,  if  several  legitimate  long-styled  plants 
were  to  fertilise  one  another,  the  average  number  of 
seeds  would  be  increased;  but  how  much  increased  I 
do  not  know;  hence  I  have  no  perfectly  fair  standard 
of  comparison  by  which  to  judge  of  the  fertility  of  the 


196  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

three  following  plants  of  the  present  lot,  the  seeds  of 
which  I  counted. 

Plant  11.  This  long-styled  plant  produced  a  large  crop 
of  capsules,  and  in  this  respect  was  one  of  the  most  fertile 
of  the  whole  lot  of  nineteen  plants.  But  the  average  from 
ten  capsules  was  only  35.9  seeds,  with  a  maximum  of  60 
and  a  minimum  of  8. 

Plant  12.  This  long-styled  plant  produced  very  few 
capsules,  and  ten  yielded  an  average  of  only  15.4  seeds, 
with  a  maximum  of  30  and  a  minimum  of  4. 

Plant  13.^  This  plant  offers  an  anomalous  case;  it  flow- 
ered profusely,  yet  produced  very  few  capsules;  but  these 
contained  numerous  seeds.  Ten  capsules  yielded  an  aver- 
age of  71.9  seeds,  with  a  maximum  of  95  and  a  minimum  of 
29.  Considering  that  this  plant  was  illegitimate  and  ille- 
gitimately fertilised  by  its  brother  long-styled  seedlings, 
the  average  and  the  maximum  are  so  remarkably  high  that 
I  cannot  at  all  understand  the  case.  We  should  remember 
that  the  average  for  a  legitimate  plant  legitimately  fertil- 


CLASS  III.  Illegitimate  Plants  raised  from  a  Short- 
styled  Parent  fertilised  with  pollen  from  own-form 
mid-length  stamens. 

I  raised  from  this  union  nine  plants,  of  which  eight 
were  short-styled  and  one  long-styled;  so  that  there 
seems  to  he  a  strong  tendency  in  this  form  to  repro- 
duce, when  self-fertilised,  the  parent- form;  but  the 
tendency  is  not  so  strong  as  with  the  long-styled. 
These  nine  plants  never  attained  the  full  height  of  le- 
gitimate plants  growing  close  to  them.  The  anthers 
were  contabescent  in  many  of  the  flowers  on  several 
plants. 

Plant  14.  This  short-styled  plant  was  allowed  during 
1865  to  be  freely  and  legitimately  fertilised  by  illegitimate 
plants  descended  from  self -fertilised  mid-,  long-,  and  short- 
styled  plants.  Fifteen  capsules  yielded  an  average  of  28.3 
seeds,  with  a  maximum  of  51  and  a  minimum  of  11.  Hence 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     197 

this  plant  produced  only  33  per  cent,  of  the  proper  number 
of  seeds.  The  seeds  themselves  were  small  and  irregular 
in  shape.  Although  so  sterile  on  the  female  side,  none 
of  the  anthers  were  contabescent. 

Plant  15.  This  short-styled  plant,  treated  like  the  last 
during  the  same  year,  yielded  an  average,  from  fifteen  cap- 
sules, of  27  seeds,  with  a  maximum  of  49  and  a  minimum 
of  7.  But  two  poor  capsules  may  be  rejected,  and  then  the 
average  rises  to  32.6,  with  the  same  maximum  of  49  and 
a  minimum  of  20;  so  that  this  plant  attained  38  per  cent, 
of  the  normal  standard  of  fertility,  and  was  rather  more 
fertile  than  the  last,  yet  many  of  the  anthers  were  con- 
tabescent. 

Plant  16.  This  short-styled  plant,  treated  like  the  two 
last,  yielded  from  ten  capsules  an  average  of  77.8  seeds, 
with  a  maximum  of  97  and  a  minimum  of  60 ;  so  that  this 
plant  produced  94  per  cent,  of  the  full  number  of  seeds. 

Plant  17.  This,  the  one  long-styled  plant  of  the  same 
parentage  as  the  last  three  plants,  when  freely  and  legiti- 
mately fertilised  in  the  same  manner  as  the  last,  yielded 
an  average  from  ten  capsules  of  76.3  rather  poor  seeds,  with 
a  maximum  of  88  and  a  minimum  of  57.  Hence  this  plant 
produced  82  per  cent,  of  the  proper  number  of  seeds. 
Twelve  flowers  enclosed  in  a  net  were  artificially  and  legiti- 
mately fertilised  with  pollen  from  a  legitimate  short-styled 
plant ;  and  nine  capsules  yielded  an  average  of  82.5  seeds, 
with  a  maximum  of  98  and  a  minimum  of  51 ;  so  that  its 
fertility  was  increased  by  the  action  of  pollen  from  a 
legitimate  plant,  but  still  did  not  reach  the  normal 
standard. 

CLASS  IV.  Illegitimate  Plants  raised  from  a  Mid-styled 
Parent  fertilised  with  pollen  from  own-form  longest 
stamens. 

After  two  trials,  I  succeeded  in  raising  only  four 
plants  from  this  illegitimate  union.  These  proved  to 
be  three  mid-styled  and  one  long-styled;  but  from  so 
small  a  number  we  can  hardly  judge  of  the  tendency 
in  mid-styled  plants  when  self-fertilised  to  reproduce 
the  same  form.  These  four  plants  never  attained  their 


198  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

full  and  normal  height;  the  long-styled  plant  had  sev- 
eral of  its  anthers  contabescent. 

Plant  18.  This  mid-styled  plant,  when  freely  and  legiti- 
mately fertilised  during  1865  by  illegitimate  plants  de- 
scended from  self-fertilised  long-,  short-,  and  mid-styled 
plants,  yielded  an  average  from  ten  capsules  of  102.6  seeds, 
with  a  maximum  of  131  and  a  minimum  of  63.  Hence  this 
plant  did  not  produce  quite  80  per  cent,  of  the  normal  num- 
ber of  seeds.  Twelve  flowers  were  artificially  and  legiti- 
mately fertilised  with  pollen  from  a  legitimate  long-styled 
plant,  and  yielded  from  nine  capsules  an  average  of  116.1 
seeds,  which  were  finer  than  in  the  previous  case,  with  a 
maximum  of  135  and  a  minimum  of  75;  so  that,  as  with 
Plant  17,  pollen  from  a  legitimate  plant  increased  the  fer- 
tility, but  did  not  bring  it  up  to  the  full  standard. 

Plant  19.  This  mid-styled  plant,  fertilised  in  the  same 
manner  and  at  the  same  period  as  the  last,  yielded  an  aver- 
age from  ten  capsules  of  73.4  seeds,  with  a  maximum  of 
87  and  a  minimum  of  64.  Hence  this  plant  produced  only 
56  per  cent,  of  the  full  number  of  seeds.  Thirteen  flowers 
were  artificially  and  legitimately  fertilised  with  pollen 
from  a  legitimate  long-styled  plant,  and  yielded  ten  cap- 
sules with  an  average  of  95.6  seeds ;  so  that  the  application 
of  pollen  from  a  legitimate  plant  added,  as  in  the  two  pre- 
vious cases,  to  the  fertility,  but  did  not  bring  it  up  to  the 
proper  standard. 

Plant  20.  This  long-styled  plant,  of  the  same  parent- 
age with  the  two  last  mid-styled  plants,  and  freely  fer- 
tilised in  the  same  manner,  yielded  an  average  from  ten 
capsules  of  69.6  seeds,  with  a  maximum  of  83  and  a  mini- 
mum of  52.  Hence  this  plant  produced  75  per  cent,  of  the 
full  number  of  seeds. 

CLASS  V.  Illegitimate  Plants  raised  from  a  Short-styled 
Parent  fertilised  with  pollen  from  the  mid-length 
stamens  of  the  long-styled  form.  t 

In  the  four  previous  classes,  plarfts  raised  from  the 
three  forms  fertilised  with  pollen  from  either  the  longer 
or  shorter  stamens  of  the  same  form,  but  generally  not 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     199 

from  the  same  plant,  have  been  described.  Six  other 
illegitimate  unions  are  possible,  namely,  between  the 
three  forms  and  the  stamens  in  the  other  two  forms 
which  do  not  correspond  in  height  with  their  pistils. 
But  I  succeeded  in  raising  plants  from  only  three  of 
these  six  unions.  From  one  of  them,  forming  the  pres- 
ent Class  V.,  twelve  plants  were  raised;  these  con- 
sisted of  eight  short-styled  and  four  long-styled  plants, 
with  not  one  mid-styled.  These  twelve  plants  never 
attained  quite  their  full  and  proper  height,  but  by  no 
means  deserved  to  be  called  dwarfs.  The  anthers  in 
some  of  the  flowers  were  contabescent.  One  plant  was 
remarkable  from  all  the  longer  stamens  in  every  flower 
and  from  many  of  the  shorter  ones  having  their 
anthers  in  this  condition.  The  pollen  of  four  other 
plants,  in  which  none  of  the  anthers  were  conta^- 
bescent,  was  examined;  in  one  a  moderate  number  of 
grains  were  minute  and  shrivelled,  but  in  the  other 
three  they  appeared  perfectly  sound.  With  respect  to 
the  power  of  producing  seed,  five  plants  (Nos.  21  to 
25)  were  observed;  one  yielded  scarcely  more  than 
half  the  normal  number;  a  second  was  slightly  infer- 
tile; butt  the  three  others  actually  produced  a  larger 
average  number  of  seeds,  with  a  higher  maximum,  than 
the  standard.  In  my  concluding  remarks  I  shall  recur 
to  this  fact,  which  at  first  appears  inexplicable. 

Plant  21.  This  short-styled  plant,  freely  and  legiti- 
mately fertilised  during  1865  by  illegitimate  plants,  de- 
scended from  self-fertilised  long-,  mid-,  and  short-styled 
parents,  yielded  an  average  from  ten  capsules  of  43  seeds, 
with  a  maximum  of  63  and  a  minimum  of  26.  Hence  this 
plant,  which  was  the  one  with  all  its  longer  and  many  of  its 
shorter  stamens  contabescent,  produced  only  52  per  cent,  of 
the  proper  number  of  seeds. 

Plant  22.  This  short-styled  plant  produced  perfectly 
sound  pollen,  as  viewed  under  the  microscope.  During 


200  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

1866  it  was  freely  and  legitimately  fertilised  by  other  ille- 
gitimate plants  belonging  to  the  present  and  the  following 
class,  both  of  which  include  many  highly  fertile  plants. 
Under  these  circumstances  it  yielded  from  eight  capsules 
an  average  of  100.5  seeds,  with  a  maximum  of  123  and  a 
minimum  of  86 ;  so  that  it  produced  121  per  cent,  of  seeds 
in  comparison  with  the  normal  standard.  During  1864  it 
was  allowed  to  be  freely  and  legitimately  fertilised  by 
legitimate  and  illegitimate  plants,  and  yielded  an  average, 
from  eight  capsules,  of  104.2  seeds,  with  a  maximum  of 
125  and  a  minimum  of  90;  consequently  it  exceeded  the 
normal  standard,  producing  125  per  cent,  of  seeds.  In  this 
case,  as  in  some  previous  cases,  pollen  from  legitimate 
plants  added  in  a  small  degree  to  the  fertility  of  the  plant ; 
and  the  fertility  would,  perhaps,  have  been  still  greater  had 
not  the  summer  of  1864  been  very  hot  and  certainly  unfa- 
vourable to  some  of  the  plants  of  Lythrum. 

Plant  28.  This  short-styled  plant  produced  perfectly 
sound  pollen.  During  1866  it  was  freely  and  legitimately 
fertilised  by  the  other  illegitimate  plants  specified  under 
the  last  experiment,  and  eight  capsules  yielded  an  average 
of  113.5  seeds,  with  a  maximum  of  123  and  a  minimum 
of  93.  Hence  this  plant  exceeded  the  normal  standard, 
producing  no  less  than  136  per  cent,  of  seeds. 

Plant  24.  This  long-styled  plant  produced  pollen  which 
seemed  under  the  microscope  sound ;  but  some  of  the  grains 
did  not  swell  when  placed  in  water.  During  1864  it  was 
legitmately  fertilised  by  legitimate  and  illegitimate  plants 
in  the  same  manner  as  Plant  22,  but  yielded  an  average, 
from  ten  capsules,  of  only  55  seeds,  with  a  maximum  of 
88  and  a  minimum  of  24,  thus  attaining  59  per  cent,  of 
the  normal  fertility.  This  low  degree  of  fertility,  I  pre- 
sume, was  owing  to  the  unfavourable  season;  for  during 
1866,  when  legitimately  fertilised  by  illegitimate  plants  in 
the  manner  described  under  No.  22,  it  yielded  an  average, 
from  eight  capsules,  of  82  seeds,  with  a  maximum  of  120 
and  a  minimum  of  67,  thus  producing  88  per  cent,  of  the 
normal  number  of  seeds. 

Plant  25.  The  pollen  of  this  long-styled  plant  contained 
a  moderate  number  of  poor  and  shrivelled  grains ;  and  this 
is  a  surprising  circumstance,  as  it  yielded  an  extraordinary 
number  of  seeds.  During  1866  it  was  freely  and  legiti- 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     201 

mately  fertilised  by  illegitimate  plants,  as  described  under 
No.  22,  and  yielded  an  average,  from  eight  capsules,  of 
122.5  seeds,  with  a  maximum  of  149  and  a  minimum  of 
84.  Hence  this  plant  exceeded  the  normal  standard,  pro- 
ducing no  less  than  131  per  cent,  of  seeds. 

CLASS  VI.  Illegitimate  Plants  raised  from  Mid-styled 
Parents  fertilised  with  pollen  from  the  shortest  sta- 
mens of  the  long-styled  form. 

I  raised  from  this  union  twenty-five  plants,  which 
proved  to  be  seventeen  long-styled  and  eight  mid- 
styled,  but  not  one  short-styled.  None  of  these  plants 
were  in  the  least  dwarfed.  I  examined,  during  the 
highly  favourable  season  of  1866,  the  pollen  of  four 
plants;  in  one  mid-styled  plant,  some  of  the  anthers  of 
the  longest  stamens  were  contabescent,  but  the  pollen- 
grains  in  the  other  anthers  were  mostly  sound,  as  they 
were  in  all  the  anthers  of  the  shortest  stamens;  in 
two  other  mid-styled  and  in  one  long-styled  plant  many 
of  the  pollen-grains  were  small  and  shrivelled;  and  in 
the  latter  plant  as  many  as  a  fifth  or  sixth  part  ap- 
peared to  be  in  this  state.  I  counted  the  seeds  in  five 
plants  (Nos.  26  to  30),  of  which  two  were  moderately 
sterile  and  three  fully  fertile. 

Plant  26.  This  mid-styled  plant  was  freely  and  legiti- 
mately fertilised,  during  the  rather  unfavourable  year 
1864,  by  numerous  surrounding  legitimate  and  illegitimate 
plants.  It  yielded  an  average,  from  ten  capsules  of  83.5 
seeds,  with  a  maximum  of  110  and  a  minimum  of  64,  thus 
attaining  64  per  cent,  of  the  normal  fertility.  During  the 
highly  favourable  year  1866,  it  was  freely  and  legitimately 
fertilised  by  illegitimate  plants  belonging  to  the  present 
Class  and  to  Class  V.,  and  yielded  an  average,  from  eight 
capsules,  of  86  seeds,  with  a  maximum  of  109  and  a  mini- 
mum of  61,  and  thus  attained  66  per  cent,  of  the  normal 
fertility.  This  was  the  plant  with  some  of  the  anthers  of 
the  longest  stamens  contabescent  as  above  mentioned. 
15 


202  ILLEGITIMATE  OFFSPRING   OF         CHAP.  V. 

Plant  27.  This  mid-styled  plant,  fertilised  during  1864 
in  the  same  manner  as  the  last,  yielded  an  average,  from 
ten  capsules,  of  99.4  seeds,  with  a  maximum  of  122  and  a 
minimum  of  53,  thus  attaining  to  76  per  cent,  of  the  normal 
fertility.  If  the  season  had  been  more  favourable,  its  fer- 
tility would  probably  have  been  somewhat  greater,  but, 
judging  from  the  last  experiment,  only  in  a  slight  de- 
gree. 

Plant  28.  This  mid-styled  plant,  when  legitimately  fer- 
tilised during  the  favourable  season  of  1866,  in  the  manner 
described  under  No.  26,  yielded  an  average,  from  eight 
capsules,  of  89  seeds,  with  a  maximum  of  119  and  a  mini- 
mum of  69,  thus  producing  68  per  cent,  of  the  full  number 
of  seeds.  In  the  pollen  of  both  sets  of  anthers,  nearly  as 
many  grains  were  small  and  shrivelled  as  sound. 

Plant  29.  This  long-styled  plant  was  legitimately  fer- 
tilised, during  the  unfavourable  season  of  1864,  in  the 
manner  described  under  No.  26,  and  yielded  an  average, 
from  ten  capsules,  of  84.6  seeds,  with  a  maximum  of  132 
and  a  minimum  of  47,  thus  attaining  to  91  per  cent,  of  the 
normal  fertility.  During  the  highly  favourable  season  of 
1866,  when  fertilised  in  the  manner  described  under  No. 
26,  it  yielded  an  average,  from  nine  capsules  (one  poor 
capsule  having  been  excluded),  of  100  seeds,  with  a  maxi- 
mum of  121  and  a  minimum  of  77.  This  plant  thus  ex- 
ceeded the  normal  standard,  and  produced  107  per  cent, 
of  seeds.  In  both  sets  of  anthers  there  were  a  good  many 
bad  and  shrivelled  pollen-grains,  but  not  so  many  as  in  the 
last-described  plant. 

Plant  SO.  This  long-styled  plant  was  legitimately  fer- 
tilised during  1866  in  the  manner  described  under  No.  26, 
and  yielded  an  average,  from  eight  capsules,  of  94  seeds, 
with  a  maximum  of  106  and  a  minimum  of  66;  so  that  it 
exceeded  the  normal  standard,  yielding  101  per  cent,  of 


Plant  31.  Some  flowers  on  this  long-styled  plant  were 
artificially  and  legitimately  fertilised  by  one  of  its  brother 
illegitimate  mid-styled  plants ;  and  five  capsules  yielded  an 
average  of  90.6  seeds,  with  a  maximum  of  97  and  a  mini- 
mum of  79.  Hence,  as  far  as  can  be  judged  from  so  few 
capsules,  this  plant  attained,  under  these  favourable  cir- 
cumstances, 98  per  cent,  of  the  normal  standard. 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     203 

CLASS  VII.  Illegitimate  Plants  raised  from  Mid-styled 
Parents  fertilised  with  pollen  from  the  longest  sta- 
mens of  the  short-styled  form. 

It  was  shown  in  the  last  chapter  that  the  union  from 
which  these  illegitimate  plants  were  raised  is  far  more 
fertile  than  any  other  illegitimate  union;  for  the  mid- 
styled  parent,  when  thus  fertilised,  yielded  an  average 
(all  very  poor  capsules  being  excluded)  of  102.8  seeds, 
with  a  maximum  of  130;  and  the  seedlings  in  the 
present  class  likewise  have  their  fertility  not  at  all 
lessened.  Forty  plants  were  raised;  and  these  attained 
their  full  height  and  were  covered  with  seed-capsules. 
Nor  did  I  observe  any  contabescent  anthers.  It  de- 
serves, also,  particular  notice  that  these  plants,  differ- 
ently from  what  occurred  in  any  of  the  previous  classes, 
consisted  of  all  three  forms,  namely,  eighteen  short- 
styled,  fourteen  long-styled,  and  eight  mid-styled 
plants.  As  these  plants  were  so  fertile,  I  counted  the 
seeds  only  in  the  two  following  cases. 

Plant  32.  This  mid-styled  plant  was  freely  and  legiti- 
mately fertilised,  during  the  unfavourable  year  of  1864, 
by  numerous  surrounding  legitimate  and  illegitimate 
plants.  Eight  capsules  yielded  an  average  of  127.2  seeds, 
with  a  maximum  of  144  and  a  minimum  of  96;  so  that 
this  plant  attained  98  per  cent,  of  the  normal  standard. 

Plant  S3.  This  short-styled  plant  was  fertilised  in  the 
same  manner  and  at  the  same  time  with  the  last ;  and  ten 
capsules  yielded  an  average  of  113.9,  with  a  maximum  of 
137  and  a  minimum  of  90.  Hence  this  plant  produced  no 
less  than  137  per  cent,  of  seeds  in  comparison  with  the 
normal  standard. 

Concluding  Remarfcs  on  the  Illegitimate  Offspring  of 
the  three  forms  of  Lythrum  salicaria. 

From  the  three  forms  occurring  in  approximately 
equal  numbers  in  a  state  of  nature,  and  from  the  re- 


204  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

suits  of  sowing  seed  naturally  produced,  there  is  reason 
to  believe  that  each  form,  when  legitimately  fertilised, 
reproduces  all  three  forms  in  about  equal  numbers. 
Now,  as  we  have  seen  (and  the  fact  is  a  very  singular 
one)  that  the  fifty-six  plants  produced  from  the 
long-styled  form,  illegitimately  fertilised  with  pollen 
from  the  same  form  (Classes  I.  and  II.),  were  all  long- 
styled.  The  short-styled  form,  when  self-fertilised 
(Class  III.),  produced  eight  short-styled  and  one  long- 
styled  plant ;  and  the  mid-styled  form,  similarly  treated 
(Class  IV.),  produced  three  mid-styled  and  one  long- 
styled  offspring;  so  that  these  two  forms,  when  ille- 
gitimately fertilised  with  pollen  from  the  same  form, 
evince  a  strong,  but  not  exclusive  tendency  to  repro- 
duce the  parent-form.  When  the  short-styled  form 
was  illegitimately  fertilised  by  the  long-styled  form 
'(Class  V.),  and  again  when  the  mid-styled  was  illegiti- 
mately fertilised  by  the  long-styled  (Class  VI.),  in 
each  case  the  two  parent-forms  alone  were  reproduced. 
As  thirty-seven  plants  were  raised  from  these  two 
unions,  we  may,  with  much  confidence,  believe  that  it 
is  the  rule  that  plants  thus  derived  usually  consist  of 
both  parent-forms,  but  not  of  the  third  form.  When, 
however,  the  mid-styled  form  was  illegitimately  fer- 
tilised by  the  longest  stamens  of  the  short-styled 
'(Class  VII.),  the  same  rule  did  not  hold  good;  for  the 
seedlings  consisted  of  all  three  forms.  The  illegiti- 
mate union  from  which  these  latter  seedlings  were 
raised  is,  as  previously  stated,  singularly  fertile,  and 
the  seedlings  themselves  exhibited  no  signs  of  sterility 
and  grew  to  their  full  height.  From  the  consideration 
of  these  several  facts,  and  from  analogous  ones  to  be 
given  under  Oxalis,  it  seems  probable  that  in  a  state 
of  nature  the  pistil  of  each  form  usually  receives, 
through  the  agency  of  insects,  pollen  from  the  stamens 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     205 

of  corresponding  height  from  both  the  other  forms. 
But  the  case  last  given  shows  that  the  application  of 
two  kinds  of  pollen  is  not  indispensable  for  the  pro- 
duction of  all  three  forms.  Hildebrand  has  suggested 
that  the  cause  of  all  three  forms  being  regularly  and 
naturally  reproduced,  may  be  that  some  of  the  flowers 
are  fertilised  with  one  kind  of  pollen,  and  others  on 
the  same  plant  with  the  other  kind  of  pollen.  Finally, 
of  the  three  forms,  the  long-styled  evinces  somewhat 
the  strongest  tendency  to  reappear  amongst  the  off- 
spring, whether  both,  or  one,  or  neither  of  the  parents 
are  long-styled. 

The  lessened  fertility  of  most  of  these  illegitimate 
plants  is  in  many  respects  a  highly  remarkable  phe- 
nomenon. Thirty-three  plants  in  the  seven  classes 
were  subjected  to  various  trials,  and  the  seeds  care- 
fully counted.  Some  of  them  were  artificially  fertil- 
ised, but  the  far  greater  number  were  freely  fertilised 
(and  this  is  the  better  and  natural  plan),  through  the 
agency  of  insects,  by  other  illegitimate  plants.  In  the 
right  hand,  or  percentage  column,  in  the  following 
table,  a  wide  difference  in  fertility  between  the  plants 
in  the  first  four  and  the  last  three  classes  may  be  per- 
ceived. In  the  first  four  classes  the  plants  are  de- 
scended from  the  three  forms  illegitimately  fertilised 
with  pollen  taken  from  the  same  form,  but  only 
rarely  from  the  same  plant.  It  is  necessary  to  observe 
this  latter  circumstance;  for,  as  I  have  elsewhere 
shown,*  most  plants,  when  fertilised  with  their  own 
pollen,  or  that  from  the  same  plant,  are  in  some 
degree  sterile,  and  the  seedlings  raised  from  such 
unions  are  likewise  in  some  degree  sterile,  dwarfed, 
and  feeble.  None  of  the  nineteen  illegitimate  plants 


*  '  The  Effects  of  Cross  and  Self-fertilisation  in  the  Vegetable  King- 
dom,' 1876. 


206 


ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 


TABLE  30. 

Tabulated  results  of  the  fertility  of  the  foregoing-  illegiti- 
mate plants,  when  legitimately  fertilised,  generally  by 
illegitimate  plants,  as  described  under  each  experiment. 
Plants  11,  12,  and  13  are  excluded,  as  they  were  illegiti- 
mately fertilised. 

Normal  Standard  of  Fertility  of  the  three  forms,  when 
legitimately  and  naturally  fertilised. 


Maximum 

Form. 

Number  of 
Seeds  per 
Capsule. 

Number  in 
any  one 
Capsule. 

Minimum  Number  in  any  one 
Capsule. 

Long-styled  .... 

93 

159 

-)  No    record    was    kept,    as 

Mid-styled    .... 

130 

151 

>     all    very    poor    capsules 

Short-styled.     .     .     . 

83.5 

112 

J      were  rejected. 

CLASSES  I.  and  II. — Illegitimate  Plants  raised  from 
Long-styled  Parents  fertilised  with  pollen  from  own- 
form  mid-length  or  shortest  stamens. 


Number  of  Plant. 

Form. 

Average 

Maximum 

Minimum 

Average  Num- 
ber of  Seeds, 
expressed  as 
the  percentage 
of  the  Normal 
Standard. 

Seeds  per 
Capsule. 

any  one 
Capsule. 

any  one 
Capsule. 

ant  1 

Long-styled 

0 

0 

0 

0 

2 

4.5 

? 

0 

5 

3 

4.5 

? 

0 

5 

4 

4.5 

? 

0 

5 

5 

Oorl 

2 

0 

Oorl 

6 

0 

0 

0 

0 

7 

36.1 

47 

22 

39 

8 

41.1 

73 

11 

44 

9 

57.1 

86 

23 

61 

10 

44.2 

69 

25 

47 

CLASS  III. — Illegitimate  Plants  raised  from  Short-styled 
Parents  fertilised  with  pollen  from  own-form  shortest 
stamens. 


Plant  14  . 

Short-styled 

28.3 

51 

11 

33 

"      15.     .. 

" 

32.6 

49 

20 

38 

"      16  ... 

M 

77.8 

97 

60 

94 

'     17.     .. 

Long-styled 

76.3 

88 

57 

82  . 

CHAP.  V.    HETEROSTYLED  TRIMORPEIC  PLANTS.     207 


TABLE  30— continued. 

CLASS  IV. — Illegitimate  Plants  raised  from  Mid-styled 
Parents  fertilised  with  pollen  from  own-form  longest 
stamens. 


Maximum 

Minimum 

Average  Nnm- 
ber  cl  Seeds, 

Number  of  Plant 

Form. 

NumbeJof 
Seeds  ]>cr 
Cap»ulo. 

Number  ia 
SSS 

Number  in 
any  ena 
Capiule. 

ezprased  a» 
the  j.crcen'ag« 
oft_eNomiil 

Plant  18  ... 

Mid-styled. 

102.6 

131 

63 

80 

"      19  ... 

44 

73.4 

87 

64 

56 

'      20  ... 

Long-styled. 

69.6 

83 

52 

75 

CLASS  V. — Illegitimate  Plants  raised  from  Short-styled 
Parents  fertilised  with  pollen  from  the  mid-length 
stamens  of  the  long-styled  form. 


Plant  21  ... 

Short-styled 

43.0 

63 

26 

52 

"     22  ... 

" 

100.5 

123 

86 

121 

"      23  ... 

11 

113.5 

123 

93 

136 

"      24.     .. 

Long-styled 

82.0 

120 

67 

88 

"      25  ... 

122.5 

149 

84 

131 

CLASS  VI. — Illegitimate  Plants  raised  from  Mid-styled 
Parents  fertilised  with  pollen  from  the  shortest  sta- 
mens of  the  long-styled  form. 


Plant  26 

Mid-styled 

86.0 

109 

61 

66 

'      27 

" 

99.4 

122 

53 

76 

'      28 

" 

89.0 

119 

69 

68 

'      29 

Long-styled 

100.0 

121 

11 

107 

'      30 

" 

94.0 

106 

66 

101 

'      31  ... 

" 

90.6 

97 

79 

98 

CLASS  VII. — Illegitimate  Plants  raised  from  Mid-styled 
Parents  fertilised  with  pollen  from  the  longest  sta- 
mens of  the  short-styled  form. 


Plant  32  . 
"      33.     .. 

Mid-styled    . 
Short-styled 

127.2 
113.9 

144 
137 

96 
90 

98 
137 

208  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

in  the  first  four  classes  were  completely  fertile;  one, 
however,  was  nearly  so,  yielding  96  per  cent,  of  the 
proper  number  of  seeds.  From  this  high  degree  of 
fertility  we  have  many  descending  gradations,  till  we 
reach  an  absolute  zero,  when  the  plants,  though  bear- 
ing many  flowers,  did  not  produce,  during  successive 
years,  a  single  seed  or  even  seed-capsule.  Some  of  the 
most  sterile  plants  did  not  even  yield  a  single  seed 
when  legitimately  fertilised  with  pollen  from  legiti- 
mate plants.  There  is  good  reason  to  believe  that  the 
first  seven  plants  in  Classes  I.  and  II.  were  the  offspring 
of  a  long-styled  plant  fertilised  with  pollen  from  its 
own-form  shortest  stamens,  and  these  plants  were  the 
most  sterile  of  all.  The  remaining  plants  in  Classes  I. 
and  II.  were  almost  certainly  the  product  of  pollen 
from  the  mid-length  stamens,  and  although  very  ster- 
ile, they  were  less  so  than  the  first  set.  None  of  the 
plants  in  the  first  four  classes  attained  their  full  and 
proper  stature;  the  first  seven,  which  were  the  most 
sterile  of  all  (as  already  stated),  were  by  far  the  most 
dwarfed,  several  of  them  never  reaching  to  half  their 
proper  height.  These  same  plants  did  not  flower  at 
so  early  an  age,  at  so  early  a  period  in  the  season, 
as  they  ought  to  have  done.  The  anthers  in  many  of 
their  flowers,  and  in  the  flowers  of  some  other  plants 
in  the  first  six  classes,  were  either  contabescent  or 
included  numerous  small  and  shrivelled  pollen-grains. 
As  the  suspicion  at  one  time  occurred  to  me  that  the 
lessened  fertility  of  the  illegitimate  plants  might  be 
due  to  the  pollen  alone  having  been  affected,  I  may 
remark  that  this  certainly  was  not  the  case;  for  several 
of  them,  when  fertilised  by  sound  pollen  from  legiti- 
mate plants,  did  not  yield  the  full  complement  of 
seeds;  hence  it  is  certain  that  both  the  female  and 
male  reproductive  organs  were  affected.  In  each  of 


CHAP.  V;    HETEROSTYLED  TRIMORPHIC  PLANTS.     209 

the  seven  classes,  the  plants,  though  descended  from 
the  same  parents,  sown  at  the  same  time  and  in  the 
same  soil,  differed  much  in  their  average  degree  of 
fertility. 

Turning  now  to  the  fifth,  sixth,  and  seventh  classes, 
and  looking  to  the  right-hand  column  of  the  table,  we 
find  nearly  as  many  plants  with  a  percentage  of  seeds 
above  the  normal  standard  as  beneath  it.  As  with 
most  plants  the  number  of  seeds  produced  varies  much, 
it  might  be  thought  that  the  present  case  was  one 
merely  of  variability.  But  this  view  must  be  rejected 
as  far  as  the  less  fertile  plants  in  these  three  classes 
are  concerned:  first,  because  none  of  the  plants  in 
Class  V.  attained  their  proper  height,  which  shows 
that  they  were  in  some  manner  affected;  and  secondly, 
because  many  of  the  plants  in  Classes  V.  and  VI.  pro- 
duced anthers  which  were  either  contabescent  or  in- 
cluded small  and  shrivelled  pollen-grains.  And  as  in 
these  cases  the  male  organs  were  manifestly  deterio- 
rated, it  is  by  far  the  most  probable  conclusion  that 
the  female  organs  were  in  some  cases  likewise  affected, 
and  that  this  was  the  cause  of  the  reduced  number  of 
seeds. 

With  respect  to  the  six  plants  in  these  three  classes 
which  yielded  a  very  high  percentage  of  seeds,  the 
thought  naturally  arises  that  the  normal  standard  of 
fertility  for  the  long-styled  and  short-styled  forms 
(with  which  alone  we  are  here  concerned)  may  have 
been  fixed  too  low,  and  that  the  six  illegitimate  plants 
are  merely  fully  fertile.  The  standard  for  the  long- 
styled  form  was  deduced  by  counting  the  seeds  in 
twenty-three  capsules,  and  for  the  short-styled  form 
from  twenty-five  capsules.  I  do  not  pretend  that  this 
is  a  sufficient  number  of  capsules  for  absolute  accu- 
racy; but  my  experience  has  led  me  to  believe  that  a 


210  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

very  fair  result  may  thus  be  gained.  As,  however,  the 
maximum  number  observed  in  the  twenty-five  capsules 
of  the  short-styled  form  was  low,  the  standard  in  this 
case  may  possibly  be  not  quite  high  enough.  But  it 
should  be  observed,  in  the  case  of  the  illegitimate 
plants,  that  in  order  to  avoid  over-estimating  their  in- 
fertility, ten  very  fine  capsules  were  always  selected; 
and  the  years  1865  and  1866,  during  which  the  plants 
in  the  three  latter  classes  were  experimented  on,  were 
highly  favourable  for  seed-production.  Now,  if  this 
plan  of  selecting  very  fine  capsules  during  favourable 
seasons  had  been  followed  for  obtaining  the  normal 
standards,  instead  of  taking,  during  various  seasons, 
the  first  capsules  which  came  to  hand,  the  standards 
would  undoubtedly  have  been  considerably  higher;  and 
thus  the  fact  of  the  six  foregoing  plants  appearing 
to  yield  an  unnaturally  high  percentage  of  seeds  may, 
perhaps,  be  explained.  On  this  view,  these  plants  are, 
in  fact,  merely  fully  fertile,  and  not  fertile  to  an  ab- 
normal degree.  Nevertheless  as  characters  of  all 
kinds  are  liable  to  variation,  especially  with  organisms 
unnaturally  treated,  and  as  in  the  four  first  and  more 
sterile  classes,  the  plants  derived  from  the  same  par- 
ents and  treated  in  the  same  manner  certainly  did 
vary  much  in  sterility,  it  is  possible  that  certain  plants 
in  the  latter  and  more  fertile  classes  may  have  varied 
so  as  to  have  acquired  an  abnormal,  degree  of  fertility. 
But  it  should  be  noticed  that,  if  my  standards  err  in 
being  too  low,  the  sterility  of  all  the  many  sterile 
plants  in  the  several  classes  will  have  to  be  estimated 
by  so  much  the  higher.  Finally,  we  see  that  the  ille- 
gitimate plants  in  the  four  first  classes  are  all  more 
or  less  sterile,  some  being  absolutely  barren,  with  one 
alone  almost  completely  fertile ;  in  the  three  latter 
classes,  some  of  the  plants  are  moderately  sterile, 


CHAP.  V.    HETEROSTYLED  TRIMORPHIC  PLANTS.     211 

whilst  others  are  fully  fertile,  or  possibly  fertile  in 
excess. 

The  last  point  which  need  here  be  noticed  is  that, 
as  far  as  the  means  of  comparison  serve,  some  degree 
of  relationship  generally  exists  between  the  infertility 
of  the  illegitimate  union  of  the  several  parent-forms 
and  that  of  their  illegitimate  offspring.  Thus  the 
two  illegitimate  unions,  from  which  the  plants  in 
Classes  VI.  and  VII.  were  derived,  yielded  a  fair 
amount  of  seed,  and  only  a  few  of  these  plants  are  in 
any  degree  sterile.  On  the  other  hand,  the  illegiti- 
mate unions  between  plants  of  the  same  form  always 
yield  very  few  seeds,  and  their  seedlings  are  very 
sterile.  Long-styled  parent-plants,  when  fertilised 
with  pollen  from  their  own-form  shortest  stamens,  ap- 
pear to  be  rather  more  sterile  than  when  fertilised  with 
their  own-form  mid-length  stamens;  and  the  seedlings 
from  the  former  union  were  much  more  sterile  than 
those  from  the  latter  union.  In  opposition  to  this  re- 
lationship, short-styled  plants  illegitimately  fertilised 
with  pollen  from  the  mid-length  stamens  of  the  long- 
styled  form  (Class  V.)  are  very  sterile;  whereas  some 
of  the  offspring  raised  from  this  union  were  far  from 
being  highly  sterile.  It  may  be  added  that  there  is  a 
tolerably  close  parallelism  in  all  the  classes  between 
the  degree  of  sterility  of  the  plants  and  their  dwarfed 
stature.  As  previously  stated,  an  illegitimate  plant 
fertilised  with  pollen  from  a  legitimate  plant  has  its 
fertility  slightly  increased.  The  importance  of  the  sev- 
eral foregoing  conclusions  will  be  apparent  at  the  close 
of  this  chapter,  when  the  illegitimate  unions  between 
the  forms  of  the  same  species  and  their  illegitimate  off- 
spring, are  compared  with  the  hybrid  unions  of  dis- 
tinct species  and  their  hybrid  offspring. 


212  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

OXALIS. 

No  one  has  compared  the  legitimate  and  illegiti- 
mate offspring  of  any  trimorphic  species  in  this  genus. 
Hildebrand  sowed  illegitimately  fertilised  seeds  of 
Oxalis  Valdiviana*  but  they  did  not  germinate;  and 
this  fact,  as  he  remarks,  supports  my  view  that  an 
illegitimate  union  resembles  a  hybrid  one  between 
two  distinct  species,  for  the  seeds  in  this  latter  case 
are  often  incapable  of  germination. 

The  following  observations  relate  to  the  nature  of  the 
forms  which  appear  among  the  legitimate  seedlings  of 
Oxalis  Valdiviana.  Hildebrand  raised,  as  described  in  the 
paper  just  referred  to,  211  seedlings  from  all  six  legiti- 
mate unions,  and  the  three  forms  appeared  among  the  off- 
spring from  each  union.  For  instance,  long-styled  plants 
were  legitimately  fertilised  with  pollen  from  the  longest 
stamens  of  the  mid-styled  form,  and  the  seedlings  con- 
sisted of  15  long-styled,  18  mid-styled,  and  6  short-styled. 
We  here  see  that  a  few  short-styled  plants  were  produced, 
though  neither  parent  was  short-styled ;  and  so  it  was  with 
the  other  legitimate  unions.  Out  of  the  above  211  seed- 
lings, 173  belonged  to  the  same  two  forms  as  their  parents, 
and  only  38  belonged  to  the  third  form  distinct  from  either 
parent.  In  the  case  of  0.  Regnelli,  the  result,  as  observed 
by  Hildebrand,  was  nearly  the  same,  but  more  striking; 
all  the  offspring  from  four  of  the  legitimate  unions  con- 
sisted of  the  two  parent-forms,  whilst  amongst  the  seed- 
lings from  the  other  two  legitimate  unions  the  third  form 
appeared.  Thus,  of  the  35  seedlings  from  the  six  legiti- 
mate unions,  35  belonged  to  the  same  two  forms  as  their 
parents,  and  only  8  to  the  third  form.  Fritz  Miiller  also 
raised  in  Brazil  seedlings  from  long-styled  plants  of  0. 
Regnelli  legitimately  fertilised  with  pollen  from  the  long- 
est stamens  of  the  mid-styled  form,  and  all  these  belonged 
to  the  two  parent-forms,  f  Lastly,  seedlings  were  raised 
by  me  from  long-styled  plants  of  0.  speciosa  legitimately 


*'Bot.   Zeitung,'   1871,   p.  433,         t  '.Tenaische    Zeitsclirift '    &c., 
footnote.  Band  vi.,  1871,  p.  75. 


CHAP.V.     HETEROSTYLED  DIMORPHIC  PLANTS.     213 

fertilised  by  the  short-styled  form,  and  from  the  latter 
reciprocally  fertilised  by  the  long-styled;  and  these  con- 
sisted of  33  long-styled  and  26  short-styled  plants  with  not 
one  mid-styled  form.  There  can,  therefore,  be  no  doubt 
that  the  legitimate  offspring  from  any  two  forms  of  Oxalis 
tend  to  belong  to  the  same  two  forms  as  their  parents ;  but 
that  a  few  seedlings  belonging  to  the  third  form  occasion- 
ally make  their  appearence;  and  this  latter  fact,  as  Hilde- 
brand  remarks,  may  be  attributed  to  atavism,  as  some  of 
their  progenitors  will  almost  certainly  have  belonged  to  the 
third  form. 

When,  however,  any  form  of  Oxalis  is  fertilised  illegiti- 
mately with  pollen  from  the  same  form,  the  seedlings  ap- 
pear to  belong  invariably  to  this  form.  Thus  Hildebrand 
states  *  that  long-styled  plants  of  0.  rosea  growing  by 
themselves  have  been  propagated  in  Germany  year  after 
year  by  seed,  and  have  always  produced  long-styled  plants. 
Again,  17  seedlings  were  raised  from  mid-styled  plants  of 
0.  hedysaroides  growing  by  themselves,  and  these  were  all 
mid-styled.  So  that  the  forms  of  Oxalis,  when  illegiti- 
mately fertilised  with  their  own  pollen,  behave  like  the 
long-styled  form  of  Lythrum  salicaria,  which  when  thus 
fertilised  always  produced  with  me  long-styled  offspring. 

PRIMULA. 
PRIMULA  SINENSIS. 

I  raised  during  February,  1862,  from  some  long- 
styled  plants  illegitimately  fertilised  with  pollen  from 
the  same  form,  twenty-seven  seedlings.  These  were 
all  long-styled.  They  proved  fully  fertile  or  even 
fertile  in  excess;  for  ten  flowers,  fertilised  with  pollen 
from  other  plants  of  the  same  lot,  yielded  nine  cap- 
sules, containing  on  an  average  39.75  seeds,  with  a 
maximum  in  one  capsule  of  66  seeds.  Four  other 
flowers  legitimately  crossed  with  pollen  from  a  legiti- 


*  '  Ueber  den  Trimorphismus  in    Berlin.'  21st  June,  1866,  p.  373; 
der    Gattung    Oxalis:      Monats-    and 'Bot.  Zeitung,' 1871,  p.  435. 
berichte  der  Akad.  der  Wissen.  zu 


214  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

mate  plant,  and  four  flowers  on  the  latter  crossed  with 
pollen  from  the  illegitimate  seedlings,  yielded  seven 
capsules  with  an  average  of  53  seeds,  with  a  maximum 
of  72.  I  must  here  state  that  I  have  found  some 
difficulty  in  estimating  the  normal  standard  of  fer- 
tility for  the  several  unions  of  this  species,  as  the  re- 
sults differ  much  during  successive  years,  and  the 
seeds  vary  so  greatly  in  size  that  it  is  hard  to  decide 
which  ought  to  be  considered  good.  In  order  to  avoid 
over-estimating  the  infertility  of  the  several  illegitimate 
unions,  I  have  taken  the  normal  standard  as  low  as 
possible. 

From  the  foregoing  twenty-seven  illegitimate  plants, 
fertilised  with  their  own-form  pollen,  twenty-five  seed- 
ling grandchildren  were  raised;  and  these  were  all 
long-styled;  so  that  from  the  two  illegitimate  gener- 
ations fifty-two  plants  were  raised,  and  all  without 
exception  proved  long-styled.  These  grandchildren 
grew  vigorously,  and  soon  exceeded  in  height  two 
other  lots  of  illegitimate  seedlings  of  different  parent- 
age and  one  lot  of  equal-styled  seedlings  presently  to 
be  described.  Hence  I  expected  that  they  would  have 
turned  out  highly  ornamental  plants;  but  when  they 
flowered,  they  seemed,  as  my  gardener  remarked,  to 
have  gone  back  to  the  wild  state;  for  the  petals  were 
pale-coloured,  narrow,  sometimes  not  touching  each 
other,  flat,  generally  deeply  notched  in  the  middle, 
but  not  flexuous  on  the  margin,  and  with  the  3?ellow 
eye  or  centre  conspicuous.  Altogether  these  flowers 
were  strikingly  different  from  those  of  their  pro- 
genitors; and  this,  I  think,  can  only  be  accounted 
for  on  the  principle  of  reversion.  Most  of  the  anthers 
on  one  plant  were  contabescent.  Seventeen  flowers 
on  the  grandchildren  were  illegitimately  fertilised 
with  pollen  taken  from  other  seedlings  of  the  same 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      215 

lot,  and  produced  fourteen  capsules,  containing  on  an 
average  29.2  seeds;  but  they  ought  to  have  con- 
tained about  35  seeds.  Fifteen  flowers  legitimately 
fertilised  with  pollen  from  an  illegitimate  short-styled 
plant  (belonging  to  the  lot  next  to  be  described)  pro- 
duced fourteen  capsules,  containing  an  average  of  46 
seeds;  they  ought  to  have  contained  at  least  50  seeds. 
Hence  these  grandchildren  of  illegitimate  descent  ap- 
pear to  have  lost,  though  only  in  a  very  slight  degree, 
their  full  fertility. 

We  will  now  turn  to  the  short-styled  form:  from  a 
plant  of  this  kind,  fertilised  with  its  own-form  pollen, 
I  raised,  during  February,  1862,  eight  seedlings,  seven 
of  which  were  short-styled  and  one  long-styled.  They 
grew  slowly,  and  never  attained  to  the  full  stature  of 
ordinary  plants;  some  of  them  flowered  precociously, 
and  others  late  in  the  season.  Four  flowers  on  these 
short-styled  seedlings  and  four  on  the  one  long-styled 
seedling  were  illegitimately  fertilised  with  their  own- 
form  pollen,  and  produced  only  three  capsules,  con- 
taining on  an  average  23.6  seeds,  with  a  maximum 
of  29;  but  we  cannot  judge  of  their  fertility  from  so 
few  capsules;  and  I  have  greater  doubts  about  the 
normal  standard  for  this  union  than  about  any  other; 
but  I  believe  that  rather  above  25  seeds  would  be  a 
fair  estimate.  Eight  flowers  on  these  same  short-styled 
plants  and  the  one  long-styled  illegitimate  plant 
were  reciprocally  and  legitimately  crossed ;  they  pro- 
duced five  capsules,  which  contained  an  average  of 
28.6  seeds,  with  a  maximum  of  36.  A  reciprocal  cross 
between  legitimate  plants  of  the  two  forms  would  have 
yielded  an  average  of  at  least  57  seeds,  with  a  possi- 
ble maximum  of  74  seeds;  so  that  these  illegitimate 
plants  were  sterile  when  legitimately  crossed. 

I  succeeded  in  raising  from  the  above  seven  short- 


216  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

styled  illegitimate  plants,  fertilised  with  their  own- 
form  pollen,  only  six  plants — grandchildren  of  the 
first  union.  These,  like  their  parents,  were  of  low 
stature,  and  had  so  poor  a  constitution  that  four  died 
before  flowering.  With  ordinary  plants  it  has  been 
a  rare  event  with  me  to  have  more  than  a  single  plant 
die  out  of  a  large  lot.  The  two  grandchildren  which 
lived  and  flowered  were  short-styled;  and  twelve  of 
their  flowers  were  fertilised  with  their  own-form  pollen 
and  produced  twelve  capsules  containing  an  average 
of  28.2  seeds;  so  that  these  two  plants,  though  be- 
longing to  so  weakly  a  set,  were  rather  more  fertile 
than  their  parents,  and  perhaps  not  in  any  degree 
sterile.  Four  flowers  on  the  same  two  grandchildren 
were  legitimately  fertilised  by  a  long-styled  illegiti- 
mate plant,  and  produced  four  capsules,  containing  only 
32.2  seeds  instead  of  about  64  seeds,  which  is  the  nor- 
mal average  for  legitimate  short-styled  plants  legiti- 
mately crossed. 

By  looking  back,  it  will  be  seen  that  I  raised  at 
first  from  a  short-styled  plant  fertilised  with  its  own- 
form  pollen  one  long-styled  and  seven  short-styled 
illegitimate  seedlings.  These  seedlings  were  legiti- 
mately intercrossed,  and  from  their  seed  fifteen  plants 
were  raised,  grandchildren  of  the  first  illegitimate 
union,  and  to  my  surprise  all  proved  short-styled. 
Twelve  short-styled  flowers  borne  by  these  grand- 
children were  illegitimately  fertilised  with  pollen 
taken  from  other  plants  of  the  same  lot,  and  produced 
eight  capsules  which  contained  an  average  of  21.8 
seeds,  with  a  maximum  of  35.  These  figures  are 
rather  below  the  normal  standard  for  such  a  union. 
Six  flowers  were  also  legitimately  fertilised  with  pollen 
from  an  illegitimate  long-styled  plant  and  produced 
only  three  capsules,  containing  on  an  average  23.6 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      217 

seeds,  with  a  maximum  of  35.  Such  a  union  in  the  case 
of  a  legitimate  plant  ought  to  have  yielded  an  average 
of  64  seeds,  with  a  possible  maximum  of  73  seeds. 

Summary  on  the  Transmission  of  Form,  Constitu- 
tion, and  Fertility  of  the  Illegitimate  Offspring  of  Pri- 
mula Sinensis. — In  regard  to  the  long-styled  plants, 
their  illegitimate  offspring,  of  which  fifty-two  were 
raised  in  the  course  of  two  generations,  were  all  long- 
styled.*  These  plants  grew  vigorously;  but  the  flowers 
in  one  instance  were  small,  appearing  as  if  they  had 
reverted  to  the  wild  state.  In  the  first  illegitimate 
generation  they  were  perfectly  fertile,  and  in  the  second 
their  fertility  was  only  very  slightly  impaired.  With 
respect  to  the  short-styled  plants,  twenty-four  out  of 
twenty-five  of  their  illegitimate  offspring  were  short- 
styled.  They  were  dwarfed  in  stature,  and  one  lot  of 
grandchildren  had  so  poor  a  constitution  that  four  out 
of  six  plants  perished  before  flowering.  The  two  sur- 
vivors, when  illegitimately  fertilised  with  their  own- 
form  pollen,  were  rather  less  fertile  than  they  ought 
to  have  been;  but  their  loss  of  fertility  was  clearly 
shown  in  a  special  and  unexpected  manner,  namely, 
when  legitimately  fertilised  by  other  illegitimate 
plants:  thus  altogether  eighteen  flowers  were  fertilised 
in  this  manner,  and  yielded  twelve  capsules,  which 
included  on  an  average  only  28.5  seeds,  with  a 
maximum  of  45.  Now,  a  legitimate  short-styled  plant 
would  have  yielded,  when  legitimately  fertilised,  an 
average  of  64  seeds,  with  a  possible  maximum  of  74. 
This  particular  kind  of  infertility  will  perhaps  be  best 
appreciated  by  a  simile:  we  may  assume  that  with 


*  Dr.     Hildebrand,    who    first  short-styled.    From  a  short-styled 

called   attention   to    this    suhject  plant  illegitimately  fertilised  with 

('  Bot.  Zeitung,'  1864,  p.  5),  raised  its  own  pollon  he  raised  fourteen 

from  a  similar  illegitimate  union  plants,  of  which  eleven  were  short- 

seventeen  plants,  of  which  four-  styled  and  three  long-styled, 
teen  were  long-styled  and  three 
16 


218  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

mankind  six  children  would  be  born  on  an  average  from 
an  ordinary  marriage;  but  that  only  three  would  be 
born  from  an  incestuous  marriage.  According  to  the 
analogy  of  Primula  Sincnsis,  the  children  of  such 
incestuous  marriages,  if  they  continued  to  marry  in- 
cestuously,  would  have  their  sterility  only  slightly  in- 
creased; but  their  fertility  would  not  be  restored 
by  a  proper  marriage;  for  if  two  children,  both  of  in- 
cestuous origin,  but  in  no  degree  related  to  each 
other,  were  to  marry,  the  marriage  would  of  course  be 
strictly  legitimate,  nevertheless  they  would  not  give 
birth  to  more  than  half  the  full  and  proper  number 
of  children. 

Equal-styled  variety  of  Primula  Sinensis. — As  any  vari- 
ation in  the  structure  of  the  reproductive  organs,  combined 
with  changed  function,  is  a  rare  event,  the  following  cases 
are  worth  giving  in  detail.  My  attention  was  first  called  to 
the  subject  by  observing,  in  1862,  a  long-styled  plant,  de- 
scended from  a  self -fertilised  long-styled  plant,  which  had 
some  of  its  flowers  in  an  anomalous  state,  namely,  with  the 
stamens  placed  low  down  in  the  corolla  as  in  the  ordinary 
long-styled  form,  but  with  the  pistils  so  short  that  the  stig- 
mas stood  on  a  level  with  the  anthers.  These  stigmas  were 
nearly  as  globular  and  as  smooth  as  in  the  short-styled 
form,  instead  of  being  elongated  and  rough  as  in  the  long- 
styled  form.  Here,  then,  we  have  combined  in  the  same 
flower,  the  short  stamens  of  the  long-styled  form  with  a 
pistil  closely  resembling  that  of  the  short-styled  form. 
But  the  structure  varied  much  even  on  the  same  umbel: 
for  in  two  flowers  the  pistil  was  intermediate  in  length  be- 
tween that  of  the  long-  and  that  of  the  short-styled  form, 
with  the  stigma  elongated  as  in  the  former,  and  smooth  as 
in  the  latter;  and  in  three  other  flowers  the  structure  was 
in  all  respects  like  that  of  the  long-styled  form.  These 
modifications  appeared  to  me  so  remarkable  that  I  fertilised 
eight  of  the  flowers  with  their  own  pollen,  and  obtained 
five  capsules,  which  contained  on  an  average  43  seeds ;  and 
this  number  shows  that  the  flowers  had  become  abnormally 
fertile  in  comparison  with  those  of  ordinary  long-styled 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.     219 


TABLE  31. 
Primula  Sinensis. 


Name  of  Owner  or  Place. 

Lolled 

Short-styled 
Form. 

•vasr 

Mr  Horwood 

o 

o 

17 

Mr  Duck   

20 

o 

9 

Baston    

30 

18 

15 

12 

g 

2 

Holwood     

42 

12 

0 

High  Elms  

16 

0 

0 

1 

5 

o 

My  own  plants  from  purchased  seeds 

13 

7 

0 

Total     

134 

51 

43 

plants  when  self -fertilised.  I  was  thus  led  to  examine  the 
plants  in  several  small  collections,  and  the  result  showed 
that  the  equal-styled  variety  was  not  rare. 

In  a  state  of  nature  the  long-  and  short-styled  forms 
would  no  doubt  occur  in  nearly  equal  numbers,  as  I  infer 
from  the  analogy  of  the  other  heterostyled  species  of 
Primula,  and  from  having  raised  the  two  forms  of  the  pres- 
ent species  in  exactly  the  same  number  from  flowers  which 
had  been  legitimately  crossed.  The  preponderance  in  the 
above  table  of  the  long-styled  form  over  the  short-styled  (in 
the  proportion  of  134  to  51)  results  from  gardeners  gener- 
ally collecting  seed  from  self -fertilised  flowers;  and  the 
long-styled  flowers  produce  spontaneously  much  more  seed 
(as  shown  in  the  first  chapter)  than  the  short-styled,  owing 
to  the  anthers  of  the  long-styled  form  being  placed  low 
down  in  the  corolla,  so  that,  when  the  flowers  fall  off,  the 
anthers  are  dragged  over  the  stigma;  and  we  now  also 
know  that  long-styled  plants,  when  self -fertilised,  very  gen- 
erally reproduce  long-styled  offspring.  From  the  con- 
sideration of  this  table,  it  occurred  to  me  in  the  year  1862, 
that  almost  all  the  plants  of  the  Chinese  primrose  culti- 
vated in  England  would  sooner  or  later  become  long-styled 
or  equal-styled;  and  now,  at  the  close  of  1876,  I  have  had 
five  small  collections  of  plants  examined,  and  almost  all 
consisted  of  long-styled,  with  some  more  or  less  well-char- 
acterised equal-styled  plants,  but  with  not  one  short-styled. 

With  respect  to  the  equal-styled  plants  in  the  table, 


220  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

Mr.  Horwood  raised  from  purchased  seeds  four  plants, 
which  he  remembered  were  certainly  not  long-styled,  but 
either  short-  or  equal-styled,  probably  the  latter.  These 
four  plants  were  kept  separate  and  allowed  to  fertilise 
themselves;  from  their  seed  the  seventeen  plants  in  the 
table  were  raised,  all  of  which  proved  equal-styled.  The 
stamens  stood  low  down  in  the  corolla  as  in  the  long-styled 
form;  and  the  stigmas,  which  were  globular  and  smooth, 
were  either  completely  surrounded  by  the  anthers,  or  stood 
close  above  them.  My  son  William  made  drawings  for 
me  by  the  aid  of  the  camera,  of  the  pollen  of  one  of  the 
above  equal-styled  plants;  and,  in  accordance  with  the 
position  of  the  stamens,  the  grains  resembled  in  their 
small  size  those  of  the  long-styled  form.  He  also  examined 
pollen  from  two  equal-styled  plants  at  Southampton;  and 
in  both  of  them  the  grains  differed  extremely  in  size  in 
the  same  anthers,  a  large  number  being  small  and  shriv- 
elled, whilst  many  were  fully  as  large  as  those  of  the  short- 
style  form  and  rather  more  globular.  It  is  probable  that 
the  large  size  of  these  grains  was  due,  not  to  their  having 
assumed  the  character  of  the  short-styled  form,  but  to  mon- 
strosity; for  Max  Wichura  has  observed  pollen-grains  of 
monstrous  size  in  certain  hybrids.  The  vast  number  of  the 
small  shrivelled  grains  in  the  above  two  cases  explains  the 
fact  that,  though  equal-styled  plants  are  generally  fertile 
in  a  high  degree,  yet  some  of  them  yield  few  seeds.  I  may 
add  that  my  son  compared,  in  1875,  the  grains  from  two 
white-flowered  plants,  in  both  of  which  the  pistil  projected 
above  the  anthers,  but  neither  were  properly  long-styled 
or  equal-styled;  and  in  the  one  in  which  the  stigma  pro- 
jected most,  the  grains  were  in  diameter  to  those  in  the 
other  plant,  in  which  the  stigma  projected  less,  as  100  to 
88;  whereas  the  difference  between  the  grains  from  per- 
fectly characterised  long-styled  and  short-styled  plants  is 
as  100  to  57.  So  that  these  two  plants  were  in  an  inter- 
mediate condition.  To  return  to  the  17  plants  in  the  first 
line  of  Table  31 :  from  the  relative  position  of  their  stig- 
mas and  anthers,  they  could  hardly  fail  to  fertilise  them- 
selves :  and  accordingly  four  of  them  spontaneously  yielded 
no  less  than  180  capsules;  of  these  Mr.  Horwood  selected 
eight  fine  capsules  for  sowing;  and  they  included  on  an 
average  54.8  seeds,  with  a  maximum  of  72.  He  gave  me 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      221 

thirty  other  capsules,  taken  by  hazard,  of  which  twenty- 
seven  contained  good  seeds,  averaging  35.5,  with  a  maxi- 
mum of  70;  but  if  six  poor  capsules,  each  with  less  than 
13  seeds,  be  excluded,  the  average  rises  to  42.5.  These  are 
higher  numbers  than  could  be  expected  from  either  well- 
characterised  form  if  self-f ertilised ;  and  this  high  degree 
of  fertility  accords  with  the  view  that  the  male  organs  be- 
longed to  one  form,  and  the  female  organs  partially  to  the 
other  form;  so  that  a  self -union  in  the  case  of  the  equal- 
styled  variety  is,  in  fact,  a  legitimate  union. 

The  seed  saved  from  the  above  seventeen  self -fertilised 
equal-styled  plants  produced  sixteen  plants,  which  all 
proved  equal-styled,  and  resembled  their  parents  in  all  the 
above-specified  respects.  The  stamens,  however,  in  one 
plant  were  seated  higher  up  the  tube  of  the  corolla  than  in 
the  true  long-styled  form;  in  another  plant  almost  all  the 
anthers  were  contabescent.  These  sixteen  plants  were  the 
grandchildren  of  the  four  original  plants  which  it  is  be- 
lieved were  equal-styled;  so  that  this  abnormal  condition 
was  faithfully  transmitted,  probably  through  three,  and 
certainly  through  two,  generations.  The  fertility  of  one 
of  these  grandchildren  was  carefully  observed;  six  flowers 
were  fertilised  with  pollen  from  the  same  flower,  and 
produced  six  capsules,  containing  on  an  average  68  seeds, 
with  a  maximum  of  82  and  a  minimum  of  40.  Thirteen 
capsules  spontaneously  self-fertilised  yielded  an  average 
of  53.2  seeds,  with  the  astonishing  maximum  in  one  of  97 
seeds.  In  no  legitimate  union  has  so  high  an  average  as 
68  seeds  been  observed  by  me,  or  nearly  so  high  a  maximum 
as  82  and  97.  These  plants,  therefore,  not  only  have  lost 
their  proper  heterostyled  structure  and  peculiar  functional 
powers,  but  have  acquired  an  abnormal  grade  of  fertility 
— unless,  indeed,  their  high  fertility  may  be  accounted  for 
by  the  stigmas  receiving  pollen  from  the  circumjacent  an- 
thers at  exactly  the  most  favourable  period. 

With  respect  to  Mr.  Duck's  lot  in  Table  31,  seed  was 
saved  from  a  single  plant,  of  which  the  form  was  not  ob- 
served, and  this  produced  nine  equal-styled  and  twenty 
long-styled  plants.  The  equal-styled  resembled  in  all  re- 
spects those  previously  described;  and  eight  of  their  cap- 
sules spontaneously  self -fertilised  contained  on  an  average 
44.4  seeds,  with  a  maximum  of  61  and  a  minimum  of  23. 


222  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

In  regard  to  the  twenty  long-styled  plants,  the  pistil  in 
some  of  the  flowers  did  not  project  quite  so  high  as  in  ordi- 
nary long-styled  flowers ;  and  the  stigmas,  though  properly 
elongated,  were  smooth,  so  that  we  have  here  a  slight  ap- 
proach in  structure  to  the  pistil  of  the  short-styled  form. 
Some  of  these  long-styled  plants  also  approached  the  equal- 
styled  in  function;  for  one  of  them  produced  no  less  than 
fifteen  spontaneously  self -fertilised  capsules,  and  of  these 
eight  contained,  on  an  average,  31.7  seeds,  with  a  maximum 
of  61.  This  average  would  be  rather  low  for  a  long-styled 
plant  artificially  fertilised  with  its  own  pollen,  but  is  high 
for  one  spontaneously  self -fertilised.  For  instance,  thirty- 
four  capsules  produced  by  the  illegitimate  grandchildren 
of  a  long-styled  plant,  spontaneously  self-fertilised,  con- 
tained on  an  average  only  9.1  seeds,  with  a  maximum  of 
46.  Some  seeds  indiscriminately  saved  from  the  foregoing 
twenty-nine  equal-styled  and  long-styled  plants  produced 
sixteen  seedlings;  grandchildren  of  the  original  plant  be- 
longing to  Mr.  Duck ;  and  these  consisted  of  fourteen  equal- 
styled  and  two  long-styled  plants ;  and  I  mention  this  fact 
as  an  additional  instance  of  the  transmission  of  the  equal- 
styled  variety. 

The  third  lot  in  the  table,  namely,  the  Baston  plants, 
are  the  last  which  need  be  mentioned.  The  long-  and  short- 
styled  plants,  and  the  fifteen  equal-styled  plants,  were  de- 
scended from  two  distinct  stocks.  The  latter  were  derived 
from  a  single  plant,  which  the  gardener  is  positive  was 
not  long-styled ;  hence  probably  it  was  equal-styled.  In  all 
these  fifteen  plants  the  anthers  occupying  the  same  posi- 
tion as  in  the  long-styled  form,  closely  surrounded  the  stig- 
ma, which  in  one  instance  alone  was  slightly  elongated. 
Notwithstanding  this  position  of  the  stigma,  the  flowers, 
as  the  gardener  assured  me,  did  not  yield  many  seeds ;  and 
this  difference  from  the  foregoing  cases  may  perhaps  have 
been  caused  by  the  pollen  being  bad,  as  in  some  of  the 
Southampton  equal-styled  plants. 

Conclusions  with  respect  to  the  equal-styled  variety 
of  P.  Sinensis.—That  this  is  a  variation,  and  not  a  third 
or  distinct  form,  as  in  the  trimorphic  genera  Ly  thrum 
and  Oxalis,  is  clear ;  for  we  have  seen  its  first  appearance 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      223 

in  one  out  of  a  lot  of  illegitimate  long-styled  plants; 
and  in  the  case  of  Mr.  Duck's  seedlings,  long-styled 
plants,  only  slightly  deviating  from  the  normal  state, 
as  well  as  equal-styled  plants  were  produced  from  the 
same  self-fertilised  parent.  The  position  of  the  sta- 
mens in  their  proper  place  low  down  in  the  tube  of 
the  corolla,  together  with  the  small  size  of  the  pollen- 
grains,  show,  firstly,  that  the  equal-styled  variety  is  a 
modification  of  the  long-styled  form,  and,  secondly,  that 
the  pistil  is  the  part  which  has  varied  most,  as  indeed 
was  obvious  in  many  of  the  plants.  This  variation  is 
of  frequent  occurrence,  and  is  strongly  inherited  when 
it  has  once  appeared.  It  would,  however,  have  pos- 
sessed little  interest  if  it  had  consisted  of  a  mere 
change  of  structure;  but  this  is  accompanied  by  modi- 
fied fertility.  Its  occurrence  apparently  stands  in 
close  relation  with  the  illegitimate  birth  of  the  parent- 
plant;  but  to  this  whole  subject  I  shall  hereafter 
recur. 

PRIMULA  AURICULA. 

Although  I  made  no  experiments  on  the  illegitimate 
offspring  of  this  species,  I  refer  to  it  for  two  reasons: — 
First,  because  I  have  observed  two  equal-styled  plants  in 
which  the  pistil  resembled  in  all  respects  that  of  the  long- 
styled  form,  whilst  the  stamens  had  become  elongated  as  in 
the  short-styled  form,  so  that  the  stigma  was  almost  sur- 
rounded by  the  anthers.  The  pollen-grains,  however,  of 
the  elongated  stamens  resembled  in  their  small  size  those 
of  the  shorter  stamens  proper  to  the  long-styled  form. 
Hence  these  plants  have  become  equal-styled  by  the  in- 
creased length  of  the  stamens,  instead  of,  as  with 'P.  Sinen- 
sis,  by  the  diminished  length  of  the  pistil.  Mr.  J.  Scott 
observed  five  other  plants  in  the  same  state,  and  he  shows  * 
that  one  of  them,  when  self-fertilised,  yielded  more  seed 
than  an  ordinary  long-  or  short-styled  form  would  have 
done  when  similarly  fertilised,  but  that  it  was  far  inferior 


*  '  Journal  Proc.  Linn.  Soc.,'  viii.  (1864),  p.  91. 


224:  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

in  fertility  to  either  form  when  legitimately  crossed. 
Hence  it  appears  that  the  male  and  female  organs  of  this 
equal-styled  variety  have  been  modified  in  some  special 
manner,  not  only  in  structure,  but  in  functional  powers. 
This,  moreover,  is  shown  by  the  singular  fact  that  both 
the  long-styled  and  short-styled  plants,  fertilised  with 
pollen  from  the  equal-styled  variety,  yield  a  lower  average 
of  seed  than  when  these  two  forms  are  fertilised  with  their 
own  pollen. 

The  second  point  which  deserves  notice  is  that  florists 
always  throw  away  the  long-styled  plants,  and  save  seed 
exclusively  from  the  short-styled  form.  Nevertheless,  as 
Mr.  Scott  was  informed  by  a  man  who  raises  this  species 
extensively  in  Scotland,  about  one-fourth  of  the  seedlings 
appear  long-styled;  so  that  the  short-styled  form  of  the 
Auricula,  when  fertilised  by  its  own  pollen,  does  not  re- 
produce the  same  form  in  so  large  a  proportion  as  in  the 
case  of  P.  Sinensis,  We  may  further  infer  that  the  short- 
styled  form  is  not  rendered  quite  sterile  by  a  long  course  of 
fertilisation  with  pollen  of  the  same  form;  but  as  there 
would  always  be  some  liability  to  an  occasional  cross  with 
the  other  form,  we  cannot  tell  how  long  self -fertilisation 
has  been  continued. 

PRIMULA  FARINOSA. 

Mr.  Scott  says  *  that  it  is  not  at  all  uncommon  to  find 
equal-styled  plants  of  this  heterostyled  species.  Judging 
from  the  size  of  the  pollen-grains,  these  plants  owe  their 
structure,  as  in  the  case  of  P.  auricula,  to  the  abnormal 
elongation  of  the  stamens  of  the  long-styled  form.  In  ac- 
cordance with  this  view,  they  yield  less  seed  when  crossed 
with  the  long-styled  form  than  with  the  short-styled.  But 
they  differ  in  an  anomalous  manner  from  the  equal-styled 
plants  of  P.  auricula  in  being  extremely  sterile  with  their 
own  pollen. 

PRIMULA  ELATIOR. 

It  was  shown  in  the  first  chapter,  on  the  authority  of 
Herr  Breitenbach,  that  equal-styled  flowers  are  occasion- 
ally found  on  this  species  whilst  growing  in  a  state  of 


'  Journal  Proc.  Linn.  Soc.,'  viii.  (1864),  p.  115. 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      225 

nature ;  and  this  is  the  only  instance  of  such  an  occurrence 
known  to  me,  with  the  exception  of  some  wild  plants  of  the 
Oxlip — a  hybrid  between  P.  veris  and  vulgaris — which 
were  equal-styled.  Herr  Breitenbach's  case  is  remarkable 
in  another  way;  for  equal-styled  flowers  were  found  in 
two  instances  on  plants  which  bore  both  long-styled  and 
short-styled  flowers.  In  every  other  instance  these  two 
forms  and  the  equal-styled  variety  have  been  produced  by 
distinct  plants. 

PRIMULA  VULGARIS,  Brit.  Fl. 
Var.  acaulls  of  Linn,  and  P.  acaulis  of  Jacq. 

Var.  rubra. — Mr.  Scott  states  *  that  this  variety, 
which  grew  in  the  Botanic  Garden  in  Edinburgh,  was 
quite  sterile  when  fertilised  with  pollen  from  the  com- 
mon primrose,  as  well  as  from  a  white  variety  of  the 
same  species,  but  that  some  of  the  plants,  when  arti- 
ficially fertilised  with  their  own  pollen,  yielded  a  moder- 
ate supply  of  seed.  He  was  so  kind  as  to  send  me  some 
of  these  self-fertilised  seeds,  from  which  I  raised  the 
plants  immediately  to  be  described.  I  may  premise 
that  the  results  of  my  experiments  on  the  seedlings, 
made  on  a  large  scale,  do  not  accord  with  those  by  Mr. 
Scott  on  the  parent-plant. 

First,  in  regard  to  the  transmission  of  form  and 
colour.  The  parent-plant  was  long-styled,  and  of  a 
rich  purple  colour.  From  the  self-fertilised  seed  23 
plants  were  raised;  of  these  18  were  purple  of  dif- 
ferent shades,  with  two  of  them  a  little  streaked  and 
freckled  with  yellow,  thus  showing  a  tendency  to 
reversion;  and  5  were  yellow,  but  generally  with  a 
brighter  orange  centre  than  in  the  wild  flower.  All 
the  plants  were  profuse  flowerers.  All  were  long- 
styled;  but  the  pistil  varied  a  good  deal  in  length 


*  'Journal  Proc.  Linn.  Soc.,'  viii.  (1864),  p. 


226  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

even  on  the  same  plant,  being  rather  shorter,  or  con- 
siderably longer,  than  in  the  normal  long-styled  form; 
and  the  stigmas  likewise  varied  in  shape.  It  is, 
therefore,  probable  that  an  equal-styled  variety  of  the 
primrose  might  be  found  on  careful  search;  and  I 
have  received  two  accounts  of  plants  apparently  in  this 
condition.  The  stamens  always  occupied  their  proper 
position  low  down  in  the  corolla;  and  the  pollen- 
grains  were  of  the  small  size  proper  to  the  long-styled 
form,  but  were  mingled  with  many  minute  and 
shrivelled  grains.  The  yellow-flowered  and  the  purple- 
flowered  plants  of  this  first  generation  were  fertilised 
under  a  net  with  their  own  pollen,  and  the  seed  sepa- 
rately sown.  From  the  former,  22  plants  were  raised 
and  all  were  yellow  and  long-styled.  From  the  latter 
or  the  purple-flowered  plants,  24  long-styled  plants 
were  raised,  of  which  17  were  purple  and  7  yellow. 
In  this  last  case  we  have  an  instance  of  reversion  in 
colour,  without  the  possibility  of  any  cross,  to  the  grand- 
parents or  more  distinct  progenitors  of  the  plants  in 
question.  Altogether  23  plants  in  the  first  generation 
and  46  in  the  second  generation  were  raised;  and  the 
whole  of  these  69  illegitimate  plants  were  long-styled! 

Eight  purple-flowered  and  two  yellow-flowered  plants 
of  the  first  illegitimate  generation  were  fertilised  in 
various  ways  with  their  own  pollen  and  with  that  of 
the  common  primrose;  and  the  seeds  were  separately 
counted,  but  as  I  could  detect  no  difference  in  fertility 
between  the  purple  and  yellow  varieties,  the  results 
are  -run  together  in  the  following  table.  (See  opposite 
page.) 

If  we  compare  the  figures  in  this  table  with  those 
given  in  the  first  chapter,  showing  the  normal  fertility 
of  the  common  primrose,  we  shall  see  that  the  illegiti- 
mate purple-  and  yellow-flowered  varieties  are  very 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      227 


TABLE  32. 
Primula  vulgaris. 


4 

J 

1| 

Li 

if 

Nature  of  Plant  experimented  on,  and 
kind  of  Union. 

If 

tf 

fc"f 

|l! 

w 

12  f 

t! 

3 

<! 

1  = 

1  * 

Purple-  and  yellow-flowered  ille-1 

gitimate  long-styled  plants,  ille-  1 
gltimately  fertilised  with  pollen  | 

72 

11 

11.5 

26 

5 

from  the  same  plant      .     .     .     .  J 

Purple-  and  yellow-flowered  ille- 

gitimate long-styled  plants,  ille- 
gitimately fertilised  Avith  pollen 

72 

39 

31.4 

62 

3 

from  the    common    long-styled 

Or,   if  the  ten  poorest  capsules,  ' 
including  less  than  15  seeds,  be 

72 

29 

40.6 

62 

18 

rejected,  we  get    

Purple-  and  yellow-flowered  ille- 

gitimate long-styled  plants,  le- 
gitimately fertilised  with  pollen 
from  the  common  short-styled 

26 

18 

36.4 

60 

9 

primrose  

Or,   if  the  two  poorest  capsules, 

including  less  than  15  seeds,  be 

26 

16 

41.2 

60 

15 

rejected,  we  get    

The  long-styled  form  of  the  com- 

mon primrose,  illegitimately  ferti- 
lised with  pollen  from  the  long- 
styled  illegitimate  purple-  and 

20 

14 

15.4 

46 

1 

yellow-flowered  plants  .... 

Or.  if  the  three  poorest  capsules 

20 

11 

18  9 

46 

8 

be  rejected,  we  get    

The  short-stvled  form  of  the  com- 

mon primrose,  legitimately  ferti- 
lised with  pollen  from  the  long- 

10 

6 

30.5 

61 

6 

styled  illegitimate  purple-  and 

yellow-flowered  plants  ..... 

sterile.  For  instance,  72  flowers  were  fertilised  with 
their  own  pollen  and  produced  only  11  good  capsules; 
but  by  the  standard  they  ought  to  have  produced  48 
capsules;  and  each  of  these  ought  to  have  contained 
on  an  average  52.2  seeds,  instead  of  only  11.5  seeds. 


228  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

When  these  plants  were  illegitimately  and  legiti- 
mately fertilised  with  pollen  from  the  common  prim- 
rose, the  average  numbers  were  increased,  but  Avere  far 
from  attaining  the  normal  standards.  So  it  was  when 
both  forms  of  the  common  primrose  were  fertilised 
with  pollen  from  these  illegitimate  plants;  and  this 
shows  that  their  male  as  well  as  their  female  organs 
were  in  a  deteriorated  condition.  The  sterility  of  these 
plants  was  shown  in  another  way,  namely,  by  their  not 
producing  any  capsules  when  the  access  of  all  insects 
(except  such  minute  ones  as  Thrips)  was  prevented; 
for  under  these  circumstances  the  common  long-styled 
primrose  produces  a  considerable  number  of  capsules. 
There  can,  therefore,  be  no  doubt  that  the  fertility  of 
these  plants  was  greatly  impaired.  The  loss  is  not 
correlated  with  the  colour  of  the  flower;  and  it  was  to 
ascertain  this  point  that  I  made  so  many  experiments. 
As  the  parent-plant  growing  in  Edinburgh  was  found 
by  Mr.  Scott  to  be  in  a  high  degree  sterile,  it  may 
have  transmitted  a  similar  tendency  to  its  offspring, 
independently  of  their  illegitimate  birth.  I  am,  how- 
ever, inclined  to  attribute  some  weight  to  the  illegiti- 
macy of  their  descent,  both  from  the  analogy  of  other 
cases,  and  more  especially  from  the  fact  that  when  the 
plants  were  legitimately  fertilised  with  pollen  of  the 
common  primrose .  they  yielded  an  average,  as  may  be 
seen  in  the  table,  of  only  5  more  seeds  than  when 
illegitimately  fertilised  with  the  same  pollen.  ISTow  we 
know  that  it  is  eminently  characteristic  of  the  illegiti- 
mate offspring  of  Primula  Sinensis  that  they  yield  but 
few  more  seeds  when  legitimately  fertilised  than  when 
fertilised  with  their  own-form  pollen. 


CHAP.  V.     HETEKOSTYLED  DIMORPHIC  PLANTS.      229 

PRIMULA  VERIS,  Brit.  Fl. 
Var.  officinalis  of  Linn.,  P.  officinalis  of  Jacq. 

Seeds  from  the  short-styled  form  of  the  cowslip 
fertilised  with  pollen  from  the  same  form  germinate 
so  badly  that  I  raised  from  three  successive  sowings 
only  fourteen  plants,  which  consisted  of  nine  short- 
styled  and  five  long-styled  plants.  Hence  the  short- 
styled  form  of  the  cowslip,  when  self -fertilised,  does  not 
transmit  the  same  form  nearly  so  truly  as  does  that 
of  P.  Sinensis.  From  the  long-styled  form,  always 
fertilised  with  its  own-form  pollen,  I  raised  in  the 
first  generation  three  long-styled  plants, — from  their 
seed  53  long-styled  grandchildren, — from  their  seed 
4  long-styled  great-grandchildren, — from  their  seed 
20  long-styled  great-great-grandchildren, — and  lastly, 
from  their  seed  8  long-styled  and  2  short-styled  great- 
great-great-grandchildren.  In  this  last  generation 
short-styled  plants  appeared  for  the  first  time  in  the 
course  of  the  six  generations, — the  parent  long-styled 
plant  which  was  fertilised  with  pollen  from  another 
plant  of  the  same  form  heing  counted  as  the  first 
generation.  Their  appearance  may  be  attributed  to 
atavism.  From  two  other  long-styled  plants,  fertilised 
with  their  own-form  pollen,  72  plants  were  raised, 
which  consisted  of  68  long-styled  and  4  short-styled. 
So  that  altogether  162  plants  were  raised  from  illegiti- 
mately fertilised  long-styled  cowslips,  and  these  con- 
sisted of  156  long-styled  and  6  short-styled  plants. 

We  will  now  turn  to  the  fertility  and  powers  of 
growth  possessed  by  the  illegitimate  plants.  From 
a  short-styled  plant,  fertilised  with  its  own-form 
pollen,  one  short-styled  and  two  long-styled  plants, 
and  from  a  long-styled  plant  similarly  fertilised  three 
long-styled  plants  were  at  first  raised.  The  fertility 


230  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

of  these  six  illegitimate  plants  was  carefully  observed; 
but  I  must  premise  that  I  cannot  give  any  satisfactory 
standard  of  comparison  as  far  as  the  number  of  the 
seeds  is  concerned;  for  though  I  counted  the  seeds 
of  many  legitimate  plants  fertilised  legitimately  and  ille- 
gitimately, the  number  varied  so  greatly  during  suc- 
cessive seasons  that  no  one  standard  will  serve  well 
for  illegitimate  unions  made  during  different  seasons. 
Moreover  the  seeds  in  the  same  capsule  frequently  differ 
so  much  in  size  that  it  is  scarcely  possible  to  decide  which 
ought  to  be  counted  as  good  seed.  There  remains  as 
the  best  standard  of  comparison  the  proportional  num- 
ber of  fertilised  flowers  which  produce  capsules  con- 
taining any  seed. 

First,  for  the  one  illegitimate  short-styled  plant. 
In  the  course  of  three  seasons  27  flowers  were  illegiti- 
mately fertilised  with  pollen  from  the  same  plant,  and 
they  yielded  only  a  single  capsule,  which,  however,  con- 
tained a  rather  large  number  of  seeds  for  a  union  of 
this  nature,  namely,  23.  As  a  standard  of  comparison 
I  may  state  that  during  the  same  three  seasons  44 
flowers  borne  by  legitimate  short-styled  plants  were 
self-fertilised,  and  yielded  26  capsules;  so  that  the 
fact  of  the  27  flowers  on  the  illegitimate  plant  having 
produced  only  one  capsule  proves  how  sterile  it  was. 
To  show  that  the  conditions  of  life  were  favourable, 
I  will  add  that  numerous  plants  of  this  and  other 
species  of  Primula  all  produced  an  abundance  of 
capsules  whilst  growing  close  by  in  the  same  soil  with 
the  present  and  following  plants.  The  sterility  of  the 
above  illegitimate  short-styled  plant  depended  on 
both  the  male  and  female  organs  being  in  a  deterio- 
rated condition.  This  was  manifestly  the  case  with 
the  pollen;  for  many  of  the  anthers  were  shrivelled 
or  contabescent.  Nevertheless  some  of  the  anthers 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      231 

contained  pollen,  with  which  I  succeeded  in  fertilising 
some  flowers  on  the  illegitimate  long-styled  plants 
immediately  to  be  described.  Four  flowers  on  this 
same  short-styled  plant  were  likewise  legitimately  fer- 
tilised with  pollen  from  one  of  the  following  long- 
styled  plants;  but  only  one  capsule  was  produced,  con- 
taining 26  seeds;  and  this  is  a  very  low  number  for  a 
legitimate  union. 

With  respect  to  the  five  illegitimate  long-styled 
plants  of  the  first  generation,  derived  from  the  above 
self-fertilised  short-styled  and  long-styled  parents, 
their  fertility  was  observed  during  the  same  three 
years.  These  five  plants,  when  self-fertilised,  differed 
considerably  from  one  another  in  their  degree  of 
fertility,  as  was  the  case  with  the  illegitimate  long- 
styled  plants  of  Lythrum  salicaria;  and  their  fertility 
varied  much  according  to  the  season.  I  may  premise, 
as  a  standard  of  comparison,  that  during  the  same 
years  56  flowers  on  legitimate  long-styled  plants  of 
the  same  age  and  grown  in  the  same  soil,  were  fer- 
tilised with  their  own  pollen,  and  yielded  27  capsules; 
that  is,  48  per  cent.  On  one  of  the  five  illegitimate 
long-styled  plants  36  flowers  were  self -fertilised  in 
the  course  of  the  three  years,  but  they  did  not  produce 
a  single  capsule.  Many  of  the  anthers  on  this  plant 
were  contabescent :  but  some  seemed  to  contain 
sound  pollen.  Nor  were  the  female  organs  quite 
impotent;  for  I  obtained  from  a  legitimate  cross  one 
capsule  with  good  seed.  On  a  second  illegitimate 
long-styled  plant  44  flowers  were  fertilised  during  the 
same  years  with  their  own  pollen,  but  they  produced 
only  a  single  capsule.  The  third  and  fourth  plants 
were  in  a  very  slight  degree  more  productive.  The 
fifth  and  last  plant  was  decidedly  more  fertile;  for 
42  self -fertilised  flowers  yielded  11  capsules.  Alto- 


232  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

gether,  in  the  course  of  the  three  years,  no  less  than 
160  flowers  on  these  five  illegitimate  long-styled  plants 
were  fertilised  with  their  own  pollen,  but  they  yielded 
only  22  capsules.  According  to  the  standard  above 
given,  they  ought  to  have  yielded  80  capsules. 

These  22  capsules  contained  on  an  average  15.1  seeds. 
I  believe,  subject  to  the  doubts  before  specified,  that 
with  legitimate  plants  the  average  number  from  a 
union  of  this  nature  would  have  been  above  20  seeds. 
Twenty-four  flowers  on  these  same  five  illegitimate 
long-styled  plants  were  legitimately  fertilised  with 
pollen  from  the  above-described  illegitimate  short- 
styled  plant,  and  produced  only  9  capsules,  which  is 
an  extremely  small  number  for  a  legitimate  union. 
These  9  capsules,  however,  contained  an  average  of  38 
apparently  good  seeds,  which  is  as  large  a  number  as 
legitimate  plants  sometimes  yield.  But  this  high  aver- 
age was  almost  certainly  false;  and  I  mention  the  case 
for  the  sake  of  showing  the  difficulty  of  arriving  at 
a  fair  result;  for  this  average  mainly  depended  on  two 
capsules  containing  the  extraordinary  numbers  of  75 
and  56  seeds;  these  seeds,  however,  though  I  felt  bound 
to  count  them,  were  so  poor  that,  judging  from  trials 
made  in  other  cases,  I  do  not  suppose  that  one  would 
have  germinated;  and  therefore  they  ought  not  to  have 
been  included.  Lastly,  20  flowers  were  legitimately  fer- 
tilised with  pollen  from  a  legitimate  plant,  and  this  in- 
creased their  fertility;  for  they  produced  10  capsules. 
Yet  this  is  but  a  very  small  proportion  for  a  legitimate 
union. 

There  can,  therefore,  be  no  doubt  that  these  five 
long-styled  plants  and  the  one  short-styled  plant  of 
the  first  illegitimate  generation  were  extremely  sterile. 
Their  sterility  was  shown,  as  in  the  case  of  hybrids, 
in  another  way,  namely,  by  their  flowering  profusely, 


CHAP.V.     HETEROSTYLED  DIMORPHIC  PLANTS.      233 

and  especially  by  the  long  endurance  of  the  flowers. 
For  instance,  I  fertilised  many  flowers  on  these  plants, 
and  fifteen  days  afterwards  (viz.  on  March  22nd)  I 
fertilised  numerous  long-styled  and  short-styled  flowers 
on  common  cowslips  growing  close  by.  These  latter 
flowers,  on  April  8th,  were  withered,  whilst  most  of  the 
illegitimate  flowers  remained  quite  fresh  for  several 
days  subsequently;  so  that  some  of  these  illegitimate 
plants,  after  being  fertilised,  remained  in  full  bloom 
for  above  a  month. 

"We  will  now  turn  to  the  fertility  of  the  53  illegiti- 
mate long-styled  grandchildren,  descended  from  the 
long-styled  plant  which  was  first  fertilised  with  its 
own  pollen.  The  pollen  in  two  of  these  plants  included 
a  multitude  of  small  and  shrivelled  grains.  Never- 
theless they  were  not  very  sterile;  for  25  flowers,  fer- 
tilised with  their  own  pollen,  produced  15  capsules, 
containing  an  average  of  16.3  seeds.  As  already 
stated,  the  probable  average  with  legitimate  plants 
for  a  union  of  this  nature  is  rather  above  20  seeds. 
These  plants  were  remarkably  healthy  and  vigorous, 
as  long  as  they  were  kept  under  highly  favourable 
conditions  in  pots  in  the  greenhouse;  and  such  treat- 
ment greatly  increases  the  fertility  of  the  cowslip. 
When  these  same  plants  were  planted  during  the  next 
year  (which,  however,  was  an  unfavourable  one),  out 
of  doors  in  good  soil,  20  self-fertilised  flowers  produced 
only  5  capsules,  containing  extremely  few  and  wretched 
seeds. 

Four  long-styled  great-grandchildren  were  raised 
from  the  self-fertilised  grandchildren,  and  were  kept 
under  the  same  highly  favourable  conditions  in  the 
greenhouse;  10  of  their  flowers  were  fertilised  with 
own-form  pollen  and  yielded  the  large  proportion  of  6 
capsules,  containing  on  an  average  18.7  seeds.  From 
17 


234  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

these  seeds  20  long-styled  great-great-grandchildren 
were  raised,  which  were  likewise  kept  in  the  greenhouse. 
Thirty  of  their  flowers  were  fertilised  with  their  own 
pollen  and  yielded  17  capsules,  containing  on  an  aver- 
age no  less  than  32  mostly  fine  seeds.  It  appears, 
therefore,  that  the  fertility  of  these  plants  of  the  fourth 
illegitimate  generation,  as  long  as  they  were  kept 
under  highly  favourable  conditions,  had  not  decreased, 
but  had  rather  increased.  The  result,  however,  was 
widely  different  when  they  were  planted  out  of  doors 
in  good  soil,  where  other  cowslips  grew  vigorously  and 
were  completely  fertile;  for  these  illegitimate  plants 
now  became  much  dwarfed  in  stature  and  extremely 
sterile,  notwithstanding  that  they  were  exposed  to  the 
visits  of  insects,  and  must  have  been  legitimately  fer- 
tilised by  the  surrounding  legitimate  plants.  A  whole 
row  of  these  plants  of  the  fourth  illegitimate  genera- 
tion, thus  freely  exposed  and  legitimately  fertilised,  pro- 
duced only  3  capsules,  containing  on  an  average  only 
17  seeds.  During  the  ensuing  winter  almost  all  these 
plants  died,  and  the  few  survivors  were  miserably  un- 
healthy, whilst  the  surrounding  legitimate  plants  were 
not  in  the  least  injured. 

The  seeds  from  the  great-great-grandchildren  were 
sown,  and  8  long-styled  and  2  short-styled  plants  of 
the  fifth  illegitimate  generation  raised.  These  whilst 
still  in  the  greenhouse  produced  smaller  leaves  and 
shorter  flower-stalks  than  some  legitimate  plants  with 
which  they  grew  in  competition;  but  it  should  be  ob- 
served that  the  latter  were  the  product  of  a  cross  with 
a  fresh  stock, — a  circumstance  which  by  itself  would 
have  added  much  to  their  vigour.*  When  these  ille- 
gitimate plants  were  transferred  to  fairly  good  soil 

*  For  full  details  of  this  experiment,  see  my  '  Effects  of  Cross  and 
Self-fertilisation,'  1876,  p.  220. 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      235 

out  of  doors,  they  became  during  the  two  following 
years  much  more  dwarfed  in  stature  and  produced  very 
few  flower-stems;  and  although  they  must  have  been 
legitimately  fertilised  by  insects,  they  yielded  capsules, 
compared  with  those  produced  by  the  surrounding  legiti- 
mate plants,  in  the  ratio  only  of  5  to  100 !  It  is  there- 
fore certain  that  illegitimate  fertilisation,  continued 
during  successive  generations,  affects  the  powers  of 
growth  and  fertility  of  P.  veris  to  an  extraordinary  de- 
gree; more  especially  when  the  plants  are  exposed  to 
ordinary  conditions  of  life,  instead  of  being  protected  in 
a  greenhouse. 

Equal-styled  red  variety  of  P.  veris. — Mr.  Scott  has 
described*  a  plant  of  this  kind  growing  in  the  Botanic  Gar- 
den of  Edinburgh.  He  states  that  it  was  highly  self -fertile, 
although  insects  were  excluded:  and  he  explains  this  fact 
by  showing,  first,  that  the  anthers  and  stigma  are  in  close 
apposition,  and  that  the  stamens  in  length,  position  and 
size  of  their  pollen-grains  resemble  those  of  the  short-styled 
form,  whilst  the  pistil  resembles  that  of  the  long-styled 
form,  both  in  length  and  in  the  structure  of  the  stigma. 
Hence  the  self-union  of  this  variety  is,  in  fact,  a  legitimate 
union,  and  consequently  is  highly  fertile.  Mr.  Scott  fur- 
ther states  that  this  variety  yielded  very  few  seeds  when 
fertilised  by  either  the  long-  or  short-styled  common  cow- 
slip, and,  again,  that  both  forms  of  the  latter,  when  fer- 
tilised by  the  equal-styled  variety,  likewise  produced  very 
few  seeds.  But  his  experiments  with  the  cowslip  were  few, 
and  my  results  do  not  confirm  his  in  any  uniform  manner. 

I  raised  twenty  plants  from  self -fertilised  seed  sent  me 
by  Mr.  Scott;  and  they  all  produced  red  flowers,  varying 
slightly  in  tint.  Of  these,  two  were  strictly  long-styled 
both  in  structure  and  in  function;  for  their  reproductive 
powers  were  tested  by  crosses  with  both  forms  of  the  com- 
mon cowslip.  Six  plants  were  equal-styled;  but  on  the 
same  plant  the  pistil  varied  a  good  deal  in  length  during 
different  seasons.  This  was  likewise  the  case,  according  to 


'Proc.  Linn.  Soc.'  vol.  viii.  (1864),  p.  105. 


236  ILLEGITIMATE  OFFSPRING  OF         CHAP.  V. 

Mr.  Scott,  with  the  parent-plant.  Lastly,  twelve  plants 
were  in  appearance  short-styled:  but  they  varied  much 
more  in  the  length  of  their  pistils  than  ordinary  short- 
styled  cowslips,  and  they  differed  widely  from  the  latter  in 
their  powers  of  reproduction.  Their  pistils  had  become 
short-styled  in  structure,  whilst  remaining  long-styled  in 
function.  Short-styled  cowslips,  when  insects  are  excluded, 
are  extremely  barren:  for  instance,  on  one  occasion  six 
fine  plants  produced  only  about  50  seeds  (that  is,  less  than 
the  product  of  two  good  capsules),  and  on  another  occasion 
not  a  single  capsule.  Now,  when  the  above  twelve  appar- 
ently short-styled  seedlings  were  similarly  treated,  nearly 
all  produced  a  great  abundance  of  capsules,  containing 
numerous  seeds,  which  germinated  remarkably  well. 
Moreover  three  of  these  plants,  which  during  the  first  year 
were  furnished  with  quite  short  pistils,  on  the  following 
year  produced  pistils  of  extraordinary  length.  The  greater 
number,  therefore,  of  these  short-styled  plants  could  not 
be  distinguished  in  function  from  the  equal-styled  variety. 
The  anthers  in  the  six  equal-styled  and  in  the  apparently 
twelve  short-styled  plants  were  seated  high  up  in  the 
corolla,  as  in  the  true  short-styled  cowslip ;  and  the  pollen- 
grains  resembled  those  of  the  same  form  in  their  large  size, 
but  were  mingled  with  a  few  shrivelled  grains.  In  function 
this  pollen  was  identical  with  that  of  the  short-styled  cow- 
slip; for  ten  long-styled  flowers  of  the  common  cowslip, 
legitimately  fertilised  with  pollen  from  a  true  equal-styled 
variety,  produced  six  capsules,  containing  on  an  average 
34.4  seeds;  whilst  seven  capsules  on  a  short-styled  cowslip 
illegitimately  fertilised  with  pollen  from  the  equal-styled 
variety,  yielded  an  average  of  only  14.5  seeds. 

As  the  equal-styled  plants  differ  from  one  another  in 
their  powers  of  reproduction,  and  as  this  is  an  important 
subject,  I  will  give  a  few  details  with  respect  to  five  of 
them.  First,  an  equal-styled  plant,  protected  from  insects 
(as  was  done  in  all  the  following  cases,  with  one  stated 
exception),  spontaneously  produced  numerous  capsules, 
five  of  which  gave  an  average  of  44.8  seeds,  with  a  maxi- 
mum in  one  capsule  of  57.  But  six  capsules,  the  product 
of  fertilisation  with  pollen  from  a  short-styled  cowslip  (and 
this  is  a  legitimate  union),  gave  an  average  of  28.5  seeds, 
with  a  maximum  of  49 ;  and  this  is  a  much  lower  average 


CHAP.  V.     HETEROSTYLED  DIMORPHIC  PLANTS.      £37 

than  might  have  been  expected.  Secondly,  nine  capsules 
from  another  equal-styled  plant,  which  had  not  been  pro- 
tected from  insects,  but  probably  was  self -fertilised,  gave 
an  average  of  45.2  seeds,  with  a  maximum  of  58.  Thirdly, 
another  plant  which  had  a  very  short  pistil  in  1865,  pro- 
duced spontaneously  many  capsules,  six  of  which  con- 
tained an  average  of  33.9  seeds,  with  a  maximum  of  38.  In 
1866  this  same  plant  had  a  pistil  of  wonderful  length ;  for  it 
projected  quite  above  the  anthers,  and  the  stigma  resem- 
bled that  of  the  long-styled  form.  In  this  condition  it  pro- 
duced spontaneously  a  vast  number  of  fine  capsules,  six  of 
which  contained  almost  exactly  the  same  average  number  as 
before,  viz.  34.3,  with  a  maximum  of  38.  Four  flowers  on 
this  plant,  legitimately  fertilised  with  pollen  from  a  short- 
styled  cowslip,  yielded  capsules  with  an  average  of  30.2 
seeds.  Fourthly,  another  short-styled  plant  spontaneously 
produced  in  1865  an  abundance  of  capsules,  ten  of  which 
contained  an  average  of  35.6  seeds,  with  a  maximum  of 
54.  In  1866  this  same  plant  had  become  in  all  respects  long- 
styled,  and  ten  capsules  gave  almost  exactly  the  same  aver- 
age as  before,  viz.  35.1  seeds,  with  a  maximum  of  47.  Eight 
flowers  on  this  plant,  legitimately  fertilised  with  pollen 
from  a  short-styled  cowslip,  produced  six  capsules,  with  the 
high  average  of  53  seeds,  and  the  high  maximum  of  67. 
Eight  flowers  were  also  fertilised  with  pollen  from  a  long- 
styled  cowslip  (this  being  an  illegitimate  union),  and  pro- 
duced seven  capsules  containing  an  average  of  24.4  seeds, 
with  a  maximum  of  32.  The  fifth  and  last  plant  remained 
in  the  same  condition  during  both  years:  it  had  a  pistil 
rather  longer  than  that  of  the  true  short-styled  form,  with 
the  stigma  smooth,  as  it  ought  to  be  in  this  form,  but 
abnormal  in  shape,  like  a  much-elongated  inverted  cone. 
It  produced  spontaneously  many  capsules,  five  of  which, 
in  1865,  gave  an  average  of  only  15.6  seeds ;  and  in  1866  ten 
capsules  still  gave  an  average  only  a  little  higher,  viz.  of 
22.1,  with  a  maximum  of  30.  Sixteen  flowers  were  ferti- 
lised with  pollen  from  a  long-styled  cowslip,  and  produced 
12  capsules,  with  an  average  of  24.9  seeds,  and  a  maximum 
of  42.  Eight  flowers  were  fertilised  with  pollen  from  a 
short-styled  cowslip,  but  yielded  only  two  capsules,  con- 
taining 18  and  23  seeds.  Hence  this  plant,  in  function  and 
partially  in  structure,  was  in  an  almost  exactly  intenne- 


238  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

diate  state  between  the  long-styled  and  short-styled  form, 
but  inclining  towards  the  short-styled;  and  this  accounts 
for  the  low  average  of  seeds  which  it  produced  when  spon- 
taneously self -fertilised. 

The  foregoing  five  plants  thus  differ  much  from  one  an- 
other in  the  nature  of  their  fertility.  In  two  individuals 
a  great  difference  in  the  length  of  the  pistil  during  two 
succeeding  years  made  no  difference  in  the  number  of  seeds 
produced.  As  all  five  plants  possessed  the  male  organs  of 
the  short-styled  form  in  a  perfect  state,  and  the  female 
organs  of  the  long-styled  form  in  a  more  or  less  complete 
state,  they  spontaneously  produced  a  surprising  number 
of  capsules,  which  generally  contained  a  large  average  of 
remarkably  fine  seeds.  With  ordinary  cowslips,  legiti- 
mately fertilised,  I  once  obtained  from  plants  cultivated 
in  the  greenhouse  the  high  average,  from  seven  capsules, 
of  58.7  seeds,  with  a  maximum  in  one  capsule  of  87  seeds ; 
but  from  plants  grown  out  of  doors  I  never  obtained  a 
higher  average  than  41  seeds.  Now  two  of  the  equal-styled 
plants,  grown  out  of  doors  and  spontaneously  self-ferti- 
lised, gave  averages  of  44  and  45  seeds;  but  this  high  fer- 
tility may  perhaps  be  in  part  attributed  to  the  stigma  re- 
ceiving pollen  from  the  surrounding  anthers  at  exactly  the 
right  period.  Two  of  these  plants,  fertilised  with  pollen 
from  a  short-styled  cowslip  (and  this  in  fact  is  a  legitimate 
union),  gave  a  lower  average  than  when  self -fertilised. 
On  the  other  hand,  another  plant,  when  similarly  fertilised 
by  a  cowslip,  yielded  the  unusually  high  average  of  53 
seeds,  with  a  maximum  of  67.  Lastly,  as  we  have  just  seen, 
one  of  these  plants  was  in  an  almost  exactly  intermediate 
condition  in  its  female  organs  between  the  long-  and  short- 
styled  forms,  and  consequently,  when  self-fertilised, 
yielded  a  lower  average  of  seed.  If  we  add  together  all 
the  experiments  which  I  made  on  the  equal-styled  plants, 
41  spontaneously  self-fertilised  capsules  (insects  having 
been  excluded)  gave  an  average  of  34  seeds,  which  is  ex- 
actly the  same  number  as  the  parent-plant  yielded  in  Edin- 
burgh. Thirty-four  flowers,  fertilised  with  pollen  from 
the  short-styled  cowslip  (and  this  is  an  analogous  union), 
produced  17  capsules,  containing  an  average  of  33.8  seeds. 
It  is  a  rather  singular  circumstance,  for  which  I  cannot 
account,  that  20  flowers,  artificially  fertilised  on  one  occa- 


CHAP.V.     HETEROSTYLED  DIMORPHIC  PLANTS.      239 

sion  with  pollen  from  the  same  plants,  yielded  only  ten 
capsules,  containing  the  low  average  of  26.7  seeds. 

As  bearing  on  inheritance,  it  may  be  added  that  72 
seedlings  were  raised  from  one  of  the  red-flowered,  strictly 
equal-styled,  self -fertilised  plants  descended  from  the  simi- 
larly characterised  Edinburgh  plant.  These  72  plants  were 
therefore  grandchildren  of  the  Edinburgh  plant,  and  they 
all  bore,  as  in  the  first  generation,  red  flowers,  with  the 
exception  of  one  plant,  which  reverted  in  colour  to  the 
common  cowslip.  In  regard  to  structure,  nine  plants  were 
truly  long-styled  and  had  their  stamens  seated  low  down  in 
the  corolla  in  the  proper  position ;  the  remaining  63  plants 
were  equal-styled,  though  the  stigma  in  about  a  dozen  of 
them  stood  a  little  below  the  anthers.  We  thus  see  that 
the  anomalous  combination  in  the  same  flower,  of  the  male 
and  female  sexual  organs  which  properly  exist  in  the  two 
distinct  forms,  was  inherited  with  much  force.  Thirty-six 
seedlings  were  also  raised  from  long-  and  short-styled 
common  cowslips,  crossed  with  pollen  from  the  equal-styled 
variety.  Of  these  plants  one  alone  was  equal-styled,  20 
were  short-styled,  but  with  the  pistil  in  three  of  them  rather 
too  long,  and  the  remaining  15  were  long-styled.  In  this 
case  we  have  an  illustration  of  the  difference  between 
simple  inheritance  and  prepotency  of  transmission;  for 
the  equal-styled  variety,  when  self -fertilised,  transmits  its 
character,  as  we  have  just  seen,  with  much  force,  but  when 
crossed  with  the  common  cowslip  cannot  withstand  the 
greater  power  of  transmission  of  the  latter. 

PULMONARIA. 

I  have  little  to  say  on  this  genus.  I  obtained  seeds  of 
P.  officinalis  from  a  garden  where  the  long-styled  form 
alone  grew,  and  raised  11  seedlings,  which  were  all  long- 
styled.  These  plants  were  named  for  me  by  Dr.  Hooker. 
They  differed,  as  has  been  shown,  from  the  plants  belong- 
ing to  this  species  which  in  Germany  were  experimented  on 
by  Hildebrand ;  *  for  he  found  that  the  long-styled  form 
was  absolutely  sterile  with  its  own  pollen,  whilst  my  long- 
styled  seedlings  and  the  parent-plants  yielded  a  fair  supply 


'  Bot.  Zeitung,'  1865,  p.  13. 


24:0  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

of  seed  when  self -fertilised.  Plants  of  the  long-styled  form 
of  Pulmonaria  angustifolia  were,  like  Hildebrand's  plants, 
absolutely  sterile  with  their  own  pollen,  so  that  I  could 
never  procure  a  single  seed.  On  the  other  hand,  the  short- 
styled  plants  of  this  species,  differently  from  those  of  P. 
officinalis,  were  fertile  with  their  own  pollen  in  a  quite  re- 
markable degree  for  a  heterostyled  plant.  From  seeds  care- 
fully self-fertilised  I  raised  18  plants,  of  which  13  proved 
short-styled  and  5  long-styled. 

POLYGONUM   FAGOPYRUM. 

From  flowers  on  long-styled  plants  fertilised  illegiti- 
mately with  pollen  from  the  same  plant,  49  seedlings  were 
raised,  and  these  consisted  of  45  long-styled  and  4  short- 
styled.  From  flowers  on  short-styled  plants  illegitimately 
fertilised  with  pollen  from  the  same  plant  33  seedlings 
were  raised,  and  these  consisted  of  20  short-styled  and  13 
long-styled.  So  that  the  usual  rule  of  illegitimately  fer- 
tilised long-styled  plants  tending  much  more  strongly  than 
short-styled  plants  to  reproduce  their  own  form  here  holds 
good.  The  illegitimate  plants  derived  from  both  forms 
flowered  later  than  the  legitimate,  and  were  to  the  latter 
in  height  as  69  to  100.  But  as  these  illegitimate  plants 
were  descended  from  parents  fertilised  with  their  own 
pollen,  whilst  the  legitimate  plants  were  descended  from 
parents  crossed  with  pollen  from  a  distinct  individual,  it  is 
impossible  to  know  how  much  of  their  difference  in  height 
and  period  of  flowering  is  due  to  the  illegitimate  birth  of 
the  one  set,  and  how  much  to  the  other  set  being  the  pro- 
duct of  a  cross  between  distinct  plants. 

Concluding  Remarks  on  the  Illegitimate  Offspring  of 
Heterostyled  Trimorphic  and  Dimorphic  Plants. 

It  is  remarkable  how  closely  and  in  how  many  points 
illegitimate  unions  between  the  two  or  three  forms  of  the 
same  heterostyled  species,  together  with  their  illegiti- 
mate offspring,  resemble  hybrid  unions  between  distinct 
species  together  with  their  hybrid  offspring.  In  both 
cases  we  meet  with  every  degree  of  sterility,  from  very 


CHAP.V.  HETEROSTYLED  PLANTS.  241 

slightly1  lessened  fertility  to  absolute  barrenness,  when 
not  even  a  single  seed-capsule  is  produced.  In  both 
cases  the  facility  of  effecting  the  first  union  is  much 
influenced  by  the  conditions  to  which  the  plants  are 
exposed.*  Both  with  hybrids  and  illegitimate  plants 
the  innate  degree  of  sterility  is  highly  variable  in 
plants  raised  from  the  same  mother-plant.  In  both 
cases  the  male  organs  are  more  plainly  affected  than 
the  female;  and  we  often  find  contabescent  anthers 
enclosing  shrivelled  and  utterly  powerless  pollen- 
grains.  The  more  sterile  hybrids,  as  Max  Wichura 
has  well  shown,  f  are  sometimes  much  dwarfed  in 
stature,  and  have  so  weak  a  constitution  that  they  are 
liable  to  premature  death;  and  we  have  seen  exactly 
parallel  cases  with  the  illegitimate  seedlings  of  Lythrum 
and  Primula.  Many  hybrids  are  the  most  persistent 
and  profuse  flowerers,  as  are  some  illegitimate  plants. 
When  a  hybrid  is  crossed  by  either  pure  parent-form, 
it  is  notoriously  much  more  fertile  than  when  crossed 
inter  se  or  by  another  hybrid;  so  when  an  illegitimate 
plant  is  fertilised  by  a  legitimate  plant,  it  is  more 
fertile  than  when  fertilised  inter  se  or  by  another  ille- 
gitimate plant.  When  two  species  are  crossed  and 
they  produced  numerous  seeds,  we  expect  as  a  general 
rule  that  their  hybrid  offspring  will  be  moderately 
fertile;  but  if  the  parent  species  produced  extremely 
few  seeds,  we  expect  that  the  hybrids  will  be  very 
sterile.  But  there  are  marked  exceptions,  as  shown 
by  Gartner,  to  these  rules.  So  it  is  with  illegitimate 
unions  and  illegitimate  offspring.  Thus  the  mid- 
styled  form  of  Lythrum  salicaria,  when  illegitimately 


*  This  has   been  remarked  by  chapter  a  striking  illustration  in 

many  experimentalists  in   effect-  the  case  of  Primula  veri*. 

ing  crosses  between  distinct  spe-  f  '  Die    Bastard befruchtung   im 

cies ;  and  in  regard  to  illegitimate  Pflanzenreich,'  1865. 
unions  I  have  given  in  the  first 


242  ILLEGITIMATE  OFFSPRING  OF        CHAP.  V. 

fertilised  with  pollen  from  the  longest  stamens  of 
the  short-styled  form,  produced  an  unusual  number 
of  seeds;  and  their  illegitimate  offspring  were  not  at 
all,  or  hardly  at  all,  sterile.  On  the  other  hand,  the 
illegitimate  offspring  from  the  long-styled  form,  ferti- 
lised with  pollen  from  the  shortest  stamens  of  the  same 
form,  yielded  few  seeds,  and  the  illegitimate  offspring 
thus  produced  were  very  sterile;  but  they  were  more 
sterile  than  might  have  been  expected  relatively  to  the 
difficulty  of  effecting  the  union  of  the  parent  sexual 
elements.  No  point  is  more  remarkable  in  regard  to 
the  crossing  of  species  than  their  unequal  reciprocity. 
Thus  species  A  will  fertilise  B  with  the  greatest  ease; 
but  B  will  not  fertilise  A  after  hundreds  of  trials.  We 
have  exactly  the  same  case  with  illegitimate  unions; 
for  the  mid-styled  Lythrum  salicaria  was  easily  ferti- 
lised by  pollen  from  the  longest  stamens  of  the  short- 
styled  form,  and  yielded  many  seeds;  but  the  latter 
form  did  not  yield  a  single  seed  when  fertilised  by  the 
longest  stamens  of  the  mid-styled  form. 

Another  important  point  is  prepotency.  Gartner 
has  shown  that  when  a  species  is  fertilised  with  pollen 
from  another  species,  if  it  be  afterwards  fertilised  with 
its  own  pollen,  or  with  that  of  the  same  species,  this 
is  so  prepotent  over  the  foreign  pollen  that  the  effect 
of  the  latter,  though  placed  on  the  stigma  some  time 
previously,  is  entirely  destroyed.  Exactly  the  same 
thing  occurs  with  the  two  forms  of  a  heterostyled 
species.  Thus  several  long-styled  flowers  of  Primula 
veris  were  fertilised  illegitimately  with  pollen  from  an- 
other plant  of  the  same  form,  and  twenty-four  hours 
afterwards  legitimately  with  pollen  from  a  short-styled 
dark-red  polyanthus  which  is  a  variety  of  P.  veris;  and 
the  result  was  that  every  one  of  the  thirty  seedlings 
thus  raised  bore  flowers  more  or  less  red,  showing  plainly 


CHAP.  V.  HETEROSTYLED  PLANTS.  243 

how  prepotent  the  legitimate  pollen  from  a  short-styled 
plant  was  over  the  illegitimate  poilen  from  a  long-styled 
plant. 

In  all  the  several  foregoing  points  the  parallelism  is 
wonderfully  close  between  the  effects  of  illegitimate 
and  hybrid  fertilisation.  It  is  hardly  an  exaggeration 
to  assert  that  seedlings  from  an  illegitimately  fer- 
tilised heterostyled  plant  are  hybrids  formed  within 
the  limits  of  one  and  the  same  species.  This  conclu- 
sion is  important,  for  we  thus  learn  that  the  difficulty 
in  sexually  uniting  two  organic  forms  and  the  sterility 
of  their  offspring,  afford  no  sure  criterion  of  so-called 
specific  distinctness.  If  any  one  were  to  cross  two 
varieties  of  the  same  form  of  Lythrum  or  Primula  for 
the  sake  of  ascertaining  whether  they  were  specifically 
distinct,  and  he  found  that  they  could  be  united  only 
with  some  difficulty,  that  their  offspring  were  extremely 
sterile,  and  that  the  parents  and  their  offspring  re- 
sembled in  a  whole  series  of  relations  crossed  species 
and  their  hybrid  offspring,  he  might  maintain  that  his 
varieties  had  been  proved  to  be  good  and  true  species; 
but  he  would  be  completely  deceived.  In  the  second 
place,  as  the  forms  of  the  same  trimorphic  or  dimorphic 
heterostyled  species  are  obviously  identical  in  general 
structure,  with  the  exception  of  the  reproductive 
organs,  and  as  they  are  identical  in  general  constitu- 
tion (for  they  live  under  precisely  the  same  condi- 
tions, the  sterility  of  their  illegitimate  unions  and  that 
of  their  illegitimate  offspring,  must  depend  exclusively 
on  the  nature  of  the  sexual  elements  and  on  their  in- 
compatibility for  uniting  in  a  particular  manner.  And 
as  we  have  just  seen  that  distinct  species  when  crossed 
resemble  in  a  whole  series  of  relations  the  forms  of  the 
same  species  when  illegitimately  united,  we  are  led  to 
conclude  that  the  sterility  of  the  former  must  likewise 


244  ILLEGITIMATE  OFFSPRING.  CHAP.  V. 

depend  exclusively  on  the  incompatible  nature  of  their 
sexual  elements,  and  not  on  any  general  difference  in 
constitution  or  structure.  We  are,  indeed,  led  to  this 
same  conclusion  by  the  impossibility  of  detecting  any 
differences  sufficient  to  account  for  certain  species  cross- 
ing with  the  greatest  ease,  whilst  other  closely  allied 
species  cannot  be  crossed,  or  can  be  crossed  only  with 
extreme  difficulty.  We  are  led  to  this  conclusion  still 
more  forcibly  by  considering  the  great  difference  which 
often  exists  in  the  facility  of  crossing  reciprocally  the 
same  two  species:  for  it  is  manifest  in  this  case  that 
the  result  must  depend  on  the  nature  of  the  sexual  ele- 
ments, the  male  element  of  the  one  species  acting  freely 
on  the  female  element  of  the  other,  but  not  so  in  a 
reversed  direction.  And  now  we  see  that  this  same  con- 
clusion is  independently  and  strongly  fortified  by  the 
consideration  of  the  illegitimate  unions  of  trimorphic 
and  dimorphic  heterostyled  plants.  In  so  complex  and 
obscure  a  subject  as  hybridism  it  is  no  slight  gain  to 
arrive  at  a  definite  conclusion,  namely,  that  we  must 
look  exclusively  to  functional  differences  in  the  sexual 
elements,  as  the  cause  of  the  sterility  of  species  when  first 
crossed  and  of  their  hybrid  offspring.  It  was  this  con- 
sideration which  led  me  to  make  the  many  observations 
recorded  in  this  chapter,  and  which  in  my  opinion  make 
them  worthy  of  publication. 


CHAP.  VI.   REMARKS  ON  HETEROSTYLED  PLANTS.  245 


CHAPTER  VI. 
CONCLUDING  EEMAEKS  ON  HETEROSTYLED  PLANTS. 

The  essential  character  of  heterostyled  plants— Summary  of  the  differ- 
ences in  fertility  between  legitimately  and  illegitimately  fertilised 
plants— Diameter  of  the  pollen-grains,  size  of  anthers  and  structure 
of  stigma  in  the  different  forms — Affinities  of  the  genera  which  in- 
clude heterostyled  species— Nature  of  the  advantages  derived  from 
heterostylism — The  means  by  which  plants  became  heterostyled — 
Transmission  of  form— Equal-styled  varieties  of  heterostyled  plants 
— Final  remarks. 

IN  the  foregoing  chapters  all  the  heterostyled  plants 
known  to  me  have  been  more  or  less  fully  described. 
Several  other  cases  have  been  indicated,  especially  by 
Professor  Asa  Gray  and  Kuhn,*  in  which  the  indi- 
viduals of  the  same  species  differ  in  the  length  of 
their  stamens  and  pistils;  but  as  I  have  been  often  de- 
ceived by  this  character  taken  alone,  it  seems  to  me 
the  more  prudent  course  not  to  rank  any  species  as 
heterostyled,  unless  we  have  evidence  of  more  impor- 
tant differences  between  the  forms,  as  in  the  diameter 
of  the  pollen-grains,  or  in  the  structure  of  the  stigma. 
The  individuals  of  many  ordinary  hermaphrodite  plants 
habitually  fertilise  one  another,  owing  to  their  male 
and  female  organs  being  mature  at  different  periods, 
or  to  the  structure  of  the  parts,  or  to  self-sterility,  &c. ; 
and  so  it  is  with  many  hermaphrodite  animals,  for 
instance,  land-snails  or  earth-worms;  but  in  all  these 
cases  any  one  individual  can  fully  fertilise  or  be  ferti- 


*  Asa  Gray,   'American  Journ.     elsewhere  as  already  referred  to. 
of   Science,'    1865,    p.    101;    and     Kuhn,  'Bot.  Zeitung,' 1867.  p.  67. 


246  CONCLUDING  REMARKS  CHAP.  VI. 

lised  by  any  other  individual  of  the  same  species.  This 
is  not  so  with  heterostyled  plants;  a  long-styled,  mid- 
styled  or  short-styled  plant  cannot  fully  fertilise  or 
be  fertilised  by  any  other  individual,  but  only  by 
one  belonging  to  another  form.  Thus  the  essen- 
tial character  of  plants  belonging  to  the  heterostyled 
class  is  that  the  individuals  are  divided  into  two  or 
three  bodies,  like  the  males  and  females  of  dioecious 
plants  or  of  the  higher  animals,  which  exist  in  approxi- 
mately equal  numbers  and  are  adapted  for  reciprocal 
fertilisation.  The  existence,  therefore,  of  two  or  three 
bodies  of  individuals,  differing  from  one  another  in  the 
above  more  important  characteristics,  offers  by  itself 
good  evidence  that  the  species  is  heterostyled.  But  ab- 
solutely conclusive  evidence  can  be  derived  only  from 
experiments,  and  by  finding  that  pollen  must  be  applied 
from  the  one  form  to  the  other  in  order  to  ensure  com- 
plete fertility. 

In  order  to  show  how  much  more  fertile  each  form 
is  when  legitimately  fertilised  with  pollen  from  the 
other  form  (or  in  the  case  of  trimorphic  species,  with 
the  proper  pollen  from  one  of  the  two  other  forms) 
than  when  illegitimately  fertilised  with  its  own-form 
pollen,  I  will  append  a  Table  (33)  giving  a  summary 
of  the  results  in  all  the  cases  hitherto  ascertained. 
The  fertility  of  the  unions  may  be  judged  by  two 
standards,  namely,  by  the  proportion  of  flowers  which, 
when  fertilised  in  the  two  methods,  yield  capsules,  and 
by  the  average  number  of  seeds  per  capsule.  When  there 
is  a  dash  in  the  left-hand  column  opposite  to  the  name 
of  the  species,  the  proportion  of  the  flowers  which  yielded 
capsules  was  not  recorded. 

The  two  or  three  forms  of  the  same  heterostyled 
species  do  not  differ  from  one  another  in  general  habit 
or  foliage,  as  sometimes,  though  rarely,  happens  with 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS. 


247 


TABLE  33. 

Fertility  of  the  Legitimate  Unions  taken  together,  com- 
pared with  that  of  the  Illegitimate  Unions  together. 
The  fertility  of  the  Legitimate  Unions,  as  judged  by 
both  standards,  is  taken  as  100. 


of  Species. 


Illegitimate  Unions. 


Primula  veris 

P.  elatior 

P.  vulgaris 

P.  Sinensis 

P.  Sinensis  (second  trial) 

P.  Sinensis  (Hildebrand) 

P.  auricula  (Scott) 

P.  Sikkhnensis  "  

P.  cortusoides  "  

P.  involuerata  "  

P.  farinosa  

Average  of  the  nine  species  of  Primula  .  . 

Hottonia  palustris  (H.  Muller) 

Linum  grandiflorum  (the  difference  probably  I 

is  much  greater) J 

L.  perenne 

L.  perenne  (Hildebrand) 

Pulmonaria  officinalis  (German  stock,  Hilde-  I 

brand)  J 

Pulmonaria  angustifolia 

Mitchella  repens 

Borreria,  Brazilian  sp 

Polygonum  fagopyrum 

Lythrum  salicaria 

Oxalis  Valdiviana  (Hildebrand) 

O.  Kegnelli  

O.  speciosa  


27 

60 
84 
0 

100 
80 
95 
74 
72 
71 
88.4 


the  two  sexes  of  dioecious  plants.  NOT  does  the  calyx 
differ,  but  the  corolla  sometimes  differs  slightly  in  shape, 
owing  to  the  different  position  of  the  anthers.  In  Bor- 
reria the  hairs  within  the  tube  of  the  corolla  are  differ- 
ently situated  in  the  long-styled  and  short-styled  forms. 
In  Pulmonaria  there  is  a  slight  difference  in  the  size  of 
the  corolla,  and  in  Pontederia  in  its  colour.  In  the  re- 


248  CONCLUDING  REMARKS  CHAP.  VI. 

productive  organs  the  differences  are  much  greater  and 
more  important.  In  the  one  form  the  stamens  may  be 
all  of  the  same  length,  and  in  the  other  graduated  in 
length,  or  alternately  longer  and  shorter.  The  fila- 
ments may  differ  in  colour  and  thickness,  and  are 
sometimes  nearly  thrice  as  long  in  the  one  form  as  in  the 
other.  They  adhere  also  for  very  different  proportional 
lengths  to  the  corolla.  The  anthers  sometimes  differ 
much  in  size  in  the  two  forms.  Owing  to  the  rotation 
of  the  filaments,  the  anthers,  when  mature,  dehisce  to- 
wards the  circumference  of  the  flower  in  one  form  of 
Faramea,  and  towards  the  centre  in  the  other  form.  The 
pollen-grains  sometimes  differ  conspicuously  in  colour, 
and  often  to  an  extraordinary  degree  in  diameter. 
They  differ  also  somewhat  in  shape,  and  apparently  in 
their  contents,  as  they  are  unequally  opaque.  In  the 
short-styled  form  of  Faramea  the  pollen-grains  are 
covered  with  sharp  points,  so  as  to  cohere  readily  to- 
gether or  to  an  insect;  whilst  the  smaller  grains  of  the 
long-styled  form  are  quite  smooth. 

With  respect  to  the  pistil,  the  style  may  be  almost 
thrice  as  long  in  the  one  form  as  in  the  other.  In 
Oxalis  it  sometimes  differs  in  hairiness  in  the  three 
forms.  In  Linum  the  pistils  either  diverge  and  pass 
out  between  the  filaments,  or  stand  nearly  upright  and 
parallel  to  them.  The  stigmas  in  the  two  forms  often 
differ  much  in  size  and  shape,  and  more  especially  in 
the  length  and  thickness  of  their  papillae;  so  that 
the  surface  may  be  rough  or  quite  smooth.  Owing 
to  the  rotation  of  the  styles,  the  papillose  surface  of 
the  stigma  is  turned  outwards  in  one  form  of  Linum 
perenne,  and  inwards  in  the  other  form.  In  flowers  of 
the  same  age  of  Primula  veris  the  ovules  are  larger  in 
the  long-styled  than  in  the  short-styled  form.  The 
seeds  produced  by  the  two  or  three  forms  often  differ 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  249 

in  number,  and  sometimes  in  size  and  weight;  thus, 
five  seeds  from  the  long-styled  form  of  Lytlirum  sali- 
caria  equal  in  weight  six  from  the  mid-styled  and  seven 
from  the  short-styled  form.  Lastly,  short-styled  plants 
of  Pulmonaria  officinalis  bear  a  larger  number  of  flow- 
ers, and  these  set  a  larger  proportional  number  of  fruit, 
which  however  yield  a  lower  average  number  of  seed, 
than  the  long-styled  plants.  With  heterostyled  plants 
we  thus  see  in  how  many  and  in  what  important  char- 
acters the  forms  of  the  same  undoubted  species  often 
differ  from  one  another — characters  which  with  ordinary 
plants  would  be  amply  sufficient  to  distinguish  species 
of  the  same  genus. 

As  the  pollen-grains  of  ordinary  species  belonging 
to  the  same  genus  generally  resemble  one  another 
closely  in  all  respects,  it  is  worth  while  to  show,  in  the 
following  table  (34),  the  difference  in  diameter  be- 
tween the  grains  from  the  two  or  three  forms  of  the 
same  heterostyled  species  in  the  forty-five  cases  in 
which  this  was  ascertained.  But  it  should  be  observed 
that  some  of  the  following  measurements  are  only 
approximately  accurate,  as  only  a  few  grains  were 
measured.  In  several  cases,  also,  the  grains  had  been 
dried  and  were  then  soaked  in  water.  Whenever  they 
were  of  an  elongated  shape  their  longer  diameters  were 
measured.  The  grains  from  the  short-styled  plants  are 
invariably  larger  than  those  from  the  long-styled,  when- 
ever there  is  any  difference  between  them.  The  diam- 
eter of  the  former  is  represented  in  the  table  by  the 
number  100. 

We  here  see  that,  with  seven  or  eight  exceptions 
out  of  the  forty-three  cases,  the  pollen-grains  from  one 
form  are  larger  than  those  from  the  other  form  of  the 
same  species.  The  extreme  difference  is  as  100  to  55, 
and  we  should  bear  in  mind  that  in  the  case  of 
18 


250 


CONCLUDING  REMARKS 


CHAP.  VI. 


TABLE  34. 

Relative  Diameter  of  the  Pollen-grains  from  the  forms 
of  the  same  Heterostyled  Species;  those  from  the 
short-styled  form  being  represented  by  100. 

Dimorphic  Species. 


Primula  veris 67 

"      vulgaris  ....     71 
"      Sinensis      (Hilde- 
brand) ....    57 
"      auricula  ....     71 
Hottonia  palustris  (H.  Miil- 
ler)    61 

Hottonia  palustris  (self)     .    64 

J  .i  ii  u  in  grandiflorum .     .    .  100 

"       perenne  (diameter  i 

variable)     .    .     j  100(?) 

"       flavum 100 

Pulmonaria  offlcinalis    .     .     78 

"  angustifolia     .    91 

Polygonum  fagopyrum  .     .     82 

Leucosmia  Burnettiana      .     99 

JEgiphila  elata 62 

Menyanthes  trifoliata  .  .  84 
Limnanthemum  Indicum  .  100 
Villarsia  (sp.  ?)  ....  75 


From  the  Long*- 
ttyled  form. 

Forsythia  suspensa      ...  94 

Cordia(sp.  ?) 100 

Gilia  pulchella 100 

"    micrantha 81 

Sethia  acuminata    ....  83 

Erythroxyluin  (sp.  ?)  .     .     .  93 

Cratoxylon  forrnosum      .     .  86 
Mitehella    repens,     pollen- 
grains  of  the  long-styled  a 
little  smaller. 

Borreria  (sp.  ?) 92 

Faramea  (sp.  ?) 67 

Sutcria  (sp.  ?)  (Fritz  Miiller)  75 

Houstonia  ccerulca  ....  72 

Oldenlandia  (sp.  ?) .     ...  78 

Hedyotis  (sp.  ?) 88 

Coccocypselum  (sp.  ?)  (F.  > 

Miiller) }  1( 

Lipostoma  (sp.  ?)....  80 

Cinchona  micrantha    ...  91 


Trimorphic  Species. 


Ratio  eTTrewiinjr  the  extreme  differences  In  diame- 
ter of  the  pollen-brains  from  the  two  sets  of 
anthers  in  the  three  formi. 

Lythrum  salicaria  ....  60 

Nessea  verticillata  ....  65 

OxalisValdiviana(Hildebrand)  71 

"  Eegnelli 78 

'  speciosa 69 

"  sensitiva 84 

Pontederia  (sp.  ?) 55 


Ratio  between  the  diameters  of  the  pollen- 
prams  of  the  two  sets  of  anthers  in  the  same 
form. 

Oxalis  rosea,  long-styled  form  ) 

(Hildebrand)    .     .     .  J  83 
'     compressa,  short-styled  i 

form I 

Pontederia  (sp.  ?)  short-styled  j 

form |  87 

"        other  sp.,  mid-styled  i 
form  . 


spheres  differing  to  this  degree  in  diameter,  their 
contents  differ  in  the  ratio  of  six  to  one.  With  all 
the  species  in  which  the  grains  differ  in  diameter, 


CHAP.  VI.         ON  HETEEOSTYLED  PLANTS.  251 

there  is  no  exception  to  the  rule  that  those  from  the 
anthers  of  the  short-styled  form,  the  tubes  of  which 
have  to  penetrate  the  longer  pistil  of  the  long-styled 
form,  are  larger  than  the  grains  from  the  other  form. 
This  curious  relation  led  Delpino  *  (as  it  formerly  did 
me)  to  believe  that  the  larger  size  of  the  grains  in 
the  short-styled  flowers  is  connected  with  the  greater 
supply  of  matter  needed  for  the  development  of  their 
longer  tubes.  But  the  case  of  Linum,  in  which 
the  grains  of  the  two  forms  are  of  equal  size,  whilst 
the  pistil  of  the  one  is  about  twice  as  long  as  that 
of  the  other,  made  me  from  the  first  feel  very 
doubtful  with  respect  to  this  view.  My  doubts  have 
since  been  strengthened  by  the  class  of  Limnanthe- 
mum  and  Coccocypselum,  in  which  the  grains  are  of 
equal  size  in  the  two  forms;  whilst  in  the  former 
genus  the  pistil  is  nearly  thrice  and  in  the  latter 
twice  as  long  as  in  the  other  form.  In  those  species 
in  which  the  grains  are  of  unequal  size  in  the  two 
forms,  there  is  no  close  relationship  between  the  de- 
gree of  their  inequality  and  that  of  their  pistils. 
Thus  in  Pulmonaria  officinalis  and  in  Erythroxy- 
lum  the  pistil  in  the  long-styled  form  is  about  twice 
the  length  of  that  in  the  other  form,  whilst  in  the 
former  species  the  pollen-grains  are  as  100  to  78,  and 
in  the  latter  as  100  to  93  in  diameter.  In  the 
two  forms  of  Suteria  the  pistil  differs  but  little  in  length, 
whilst  the  pollen-grains  are  as  100  to  75  in  diameter. 
These  cases  seem  to  prove  that  the  difference  in  size 
between  the  grains  in  the  two  forms  is  not  deter- 
mined by  the  length  of  the  pistil,  down  which  the 
tubes  have  to  grow.  That  with  plants  in  general  there 
is  no  close  relationship  between  the  size  of  the  pollen- 


*  'Sull'  Opera,  la  Distribuzione  dei  Sessi  nelle  Piante,'  &c.,  1867, 
p.  17. 


252  CONCLUDING  REMARKS  CHAP.  VI. 

grains  and  the  length  of  the  pistil  is  manifest;  for 
instance,  I  found  that  the  distended  grains  of  Datura 
arborea  were  .00243  of  an  inch  in  diameter,  and  the 
pistil  no  less  than  9.25  inches  in  length;  now  the 
pistil  in  the  small  flowers  of  Polygonum  fagopyrum 
is  very  short,  yet  the  larger  pollen-grains  from  the  short- 
styled  plants  had  exactly  the  same  diameter  as  those 
from  the  Datura,  with  its  enormously  elongated 
pistil. 

Notwithstanding  these  several  considerations,  it  is 
difficult  quite  to  give  up  the  belief  that  the  pollen-grains 
from  the  longer  stamens  of  heterostyled  plants  have 
become  larger  in  order  to  allow  of  the  development  of 
longer  tubes;  and  the  foregoing  opposing  facts  may 
possibly  be  reconciled  in  the  following  manner.  The 
tubes  are  at  first  developed  from  matter  contained 
within  the  grains,  for  they  are  sometimes  exserted  to 
a  considerable  length,  before  the  grains  have  touched 
the  stigma;  but  botanists  believe  that  they  afterwards 
draw  nourishment  from  the  conducting  tissue  of 
the  pistil.  It  is  hardly  possible  to  doubt  that  this 
must  occur  in  such  cases  as  that  of  the  Datura,  in 
which  the  tubes  have  to  grow  down  the  whole  length 
of  the  pistil,  and  therefore  to  a  length  equalling  3,806 
times  the  diameter  of  the  grains  (namely,  .00243  of 
an  inch)  from  which  they  are  protruded.  I  may  here 
remark  that  I  have  seen  the  pollen-grains  of  a  willow, 
immersed  in  a  very  weak  solution  of  honey,  protrude 
their  tubes,  in  the  course  of  twelve  hours,  to  a  length 
thirteen  times  as  great  as  the  diameter  of  the  grains. 
Now,  if  we  suppose  that  the  tubes  in  some  heterostyled 
species  are  developed  wholly  or  almost  wholly  from 
matter  contained  within  the  grains,  while  in  other  spe- 
cies from  matter  yielded  by  the  pistil,  we  can  see  that 
in  the  former  case  it  would  be  necessary  that  the  grains 


CHAP.  VI.        ON  HETEROSTYLED  PLANTS.  253 

of  the  two  forms  should  differ  in  size  relatively  tq  the 
length  of  the  pistil  which  the  tubes  have  to  penetrate, 
but  that  in  the  latter  case  it  would  not  be  necessary 
that  the  grains  should  thus  differ.  Whether  this  expla- 
nation can  be  considered  satisfactory  must  remain  at 
present  doubtful. 

There  is  another  remarkable  difference  between 
the  forms  of  several  heterostyled  species,  namely  in  the 
anthers  of  the  short-styled  flowers,  which  contain  the 
larger  pollen-grains,  being  longer  than  those  of  the 
long-styled  flowers.  This  is  the  case  with  Hottonia 
palustris  in  the  ratio  of  100  to  83.  With  Lvmnan- 
themum  Indicum  the  ratio  is  as  100  to  70.  With  the 
allied  Menyanthes  the  anthers  of  the  short-styled  form 
are  a  little  and  with  Villarsia  conspicuously  larger 
than  those  of  the  long-styled.  With  Pulmonaria  an- 
gustifolia  they  vary  much  in  size,  but  from  an  aver- 
age of  seven  measurements  of  each  kind  the  ratio 
is  as  100  to  91.  In  six  genera  of  the  Eubiaceae  there 
is  a  similar  difference,  either  slightly  or  well  marked. 
Lastly,  in  the  trimorphic  Pontederia  the  ratio  is  100 
to  88;  the  anthers  from  the  longest  stamens  in  the 
short-styled  form  being  compared  with  those  from  the 
shortest  stamens  in  the  long-styled  form.  On  the  other 
hand,  there  is  a  similar  and  well-marked  difference 
in  the  length  of  the  stamens  in  the  two  forms  of 
Forsythia  suspensa  and  of  Unum  flavum;  but  in  these 
two  cases  the  anthers  of  the  short-styled  flowers  are 
shorter  than  those  of  the  long-styled.  The  relative 
size  of  the  anthers  was  not  particularly  attended  to  in 
the  two  forms  of  the  other  heterostyled  plants,  but 
I  believe  that  they  are  generally  equal,  as  is  certainly 
the  case  with  those  of  the  common  primrose  and 
cowslip. 

The  pistil  differs  in  length  in  the  two  forms  of  every 


254  CONCLUDING  REMARKS  CHAP.  VI. 

heterostyled  plant,  and  although  a  similar  difference 
is  very  general  with  the  stamens,  yet  in  the  two 
forms  of  Linum  grandiflorum*  and  of  Cordia  they  are 
equal.  There  can  hardly  be  a  doubt  that  the  rela- 
tive length  of  these  organs  is  an  adaptation  for  the 
safe  transportal  by  insects  of  the  pollen  from  the  one 
form  to  the  other.  The  exceptional  cases  in  which 
these  organs  do  not  stand  exactly  on  a  level  in  the  two 
forms  may  probably  be  explained  by  the  manner  in 
which  the  flowers  are  visited.  With  most  of  the 
species,  if  there  is  any  difference  in  the  size  of  the 
stigma  in  the  two  forms,  that  of  the  long-styled,  what- 
ever its  shape  may  be,  is  larger  than  that  of  the  short- 
styled.  But  here  again  there  are  some  exceptions  to 
the  rule,  for  in  the  short-styled  form  of  Leucosmia 
Burnettiana  the  stigmas  are  longer  and  much  narrower 
than  those  of  the  long-styled;  the  ratio  between  the 
lengths  of  the  stigmas  in  the  two  forms  being  100  to  60. 
In  the  three  Rubiaceous  genera,  Faramea,  Houstonia, 
and  Oldenlandia,  the  stigmas  of  the  short-styled  form 
are  likewise  somewhat  longer  and  narrower;  and  in 
the  three  forms  of  Oxalis  sensitiva  the  difference  is 
strongly  marked,  for  if  the  length  of  the  two  stigmas 
of  the  long-styled  pistil  be  taken  as  100,  it  will  be 
represented  in  the  mid-  and  short-styled  forms  by 
the  numbers  141  and  164.  As  in  all  these  cases  the 
stigmas  of  the  short-styled  pistil  are  seated  low  down 
within  a  more  or  less  tubular  corolla,  it  is  probable  that 
they  are  better  fitted  by  being  long  and  narrow  for 
brushing  the  pollen  off  the  inserted  proboscis  of  an 
insect. 

With  many  heterostyled  plants  the  stigma  differs 
in  roughness  in  the  two  forms,  and  when  this  is  the 
case  there  is  no  known  exception  to  the  rule  that  the 
papilla?  on  the  stigma  of  the  long-styled  form  are  longer 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  255 

and  often  thicker  than  those  on  that  of  the  short- 
styled.  For  instance,  the  papillae  on  the  long-styled 
stigma  of  Hottonia  palustris  are  more  than  twice  the 
length  of  those  in  the  other  form.  This  holds  good 
even  in  the  case  of  Houstonia  ccerulea,  in  which  the 
stigmas  are  much  shorter  and  stouter  in  the  long- 
styled  than  in  the  short-styled  form,  for  the  papillae 
on  the  former  compared  with  those  on  the  latter  are 
as  100  to  58  in  length.  The  length  of  the  pistil 
in  the  long-styled  form  of  Linum  grandiflorum  varies 
much,  and  the  stigmatic  papillae  vary  in  a  corre- 
sponding manner.  From  this  fact  I  inferred  at  first 
that  in  all  cases  the  difference  in  length  between  the 
stigmatic  papillaB  in  the  two  forms  was  one  merely  of 
correlated  growth;  but  this  can  hardly  be  the  true  or 
general  explanation,  as  the  shorter  stigmas  of  the 
long-styled  form  of  Houstonia  have  the  longer  papillae. 
It  is  a  more  probable  view  that  the  papilla?,  which  ren- 
der the  stigma  of  the  long-styled  form  of  various  species 
rough,  serve  to  entangle  effectually  the  large-sized  pol- 
len-grains brought  by  insects  from  the  short-styled  form, 
thus  ensuring  its  legitimate  fertilisation.  This  view  is 
supported  by  the  fact  that  the  pollen-grains  from  the 
two  forms  of  eight  species  in  Table  34  hardly  differ  in 
diameter,  and  the  papillaa  on  their  stigmas  do  not  differ 
in  length. 

The  species  which  are  at  present  positively  or  almost 
positively  known  to  be  heterostyled  belong,  as  shown  in 
the  following  table,  to  38  genera,  widely  distributed, 
throughout  the  world.  These  genera  are  included  in 
fourteen  Families,  most  of  which  are  very  distinct  from 
one  another,  for  they  belong  to  nine  of  the  several  great 
Series,  into  which  phanerogamic  plants  have  been  di- 
vided by  Bentham  and  Hooker. 


256 


CONCLUDING  REMARKS 


CHAP.  VI. 


TABLE  35. 
List  of  Genera  including  Heterostyled  Species. 


DlCOT 

FLEDONS. 

DICOTYLEDONS. 

Cratoxylon. 

Hypericinese. 

Mitchella.             Eubiacese. 

Erythroxylum. 

Erytnroxylese. 

Diodia. 

Sethia. 

" 

Borreria. 

Linum. 

Geraniacese. 

Spermacoce. 

Oxalis. 

" 

Primula.               Primulacese. 

Lythrum. 

Lythracero. 

Hottonia. 

Nessea. 

" 

Androsace. 

Cinchona. 

Rubiaceae. 

Forsythia.             Oleaceae. 

Bouvardia. 

1 

Menyanthes.        Gentianacese. 

Manettia. 

' 

Limnantlicmiiin.           " 

Hedyotis. 

1 

Villarsia. 

Oldenlandia. 

1 

Gilia.                     Polemoniacea 

Houstonia. 

' 

Cordia.                  Cordieae. 

Coccocypselum. 

1 

Pulmonaria.         Boragineae. 

Lipostoma. 

1 

^Egiphila.              Verbenaceae. 

Knoxia. 

4 

Polygonum.          Polygonese. 

Faramea. 

1 

Thynielea.            Tkymelese. 

Psychotria. 
Eudgea. 

. 

MONOCOTYLEDONS. 

Suteria. 

" 

Pontederia.          Pontederiaces 

In  some  of  these  families  the  heterostyled  condition 
must  have  been  acquired  at  a  very  remote  period. 
Thus  the  three  closely  allied  genera,  Menyanthes, 
Limnanthemum,  and  Villarsia,  inhabit  respectively 
Europe,  India,  and  South  America.  Heterostyled  spe- 
cies of  Hedyotis  are  found  in  the  temperate  regions 
of  North  and  the  tropical  regions  of  South  America. 
Trimorphic  species  of  Oxalis  live  on  both  sides  of 
the  Cordillera  in  South  America  and  at  the  Cape  of 
Good  Hope.  In  these  and  some  other  cases  it  is  not 
probable  that  each  species  acquired  its  heterostyled 
structure  independently  of  its  close  allies.  If  they 
did  not  do  so,  the  three  closely  connected  genera  of 
the  Menyanthese  and  the  several  trimorphic  species  of 
Oxalis  must  have  inherited  their  structure  from  a 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  257 

common  progenitor.  But  an  immense  lapse  of  time 
will  have  been  necessary  in  all  such  cases  for  the 
modified  descendants  of  a  common  progenitor  to  have 
spread  from  a  single  centre  to  such  widely  remote  and 
separated  areas.  The  family  of  the  Rubiaceae  contains 
not  far  short  of  as  many  heterostyled  genera  as  all  the 
other  thirteen  families  together ;  and  hereafter  no  doubt 
other  Eubiaceous  genera  will  be  found  to  be  hetero- 
styled, although  a  large  majority  are  homostyled.  Sev- 
eral closely  allied  genera  in  this  family  probably  owe 
their  heterostyled  structure  to  descent  in  common;  but 
as  the  genera  thus  characterised  are  distributed  in  no 
less  than  eight  of  the  tribes  into  which  this  family  has 
been  divided  by  Bentham  and  Hooker,  it  is  almost 
certain  that  several  of  them  must  have  become  het- 
erostyled independently  of  one  another.  What  there 
is  in  the  constitution  or  structure  of  the  members  of 
this  family  which  favours  their  becoming  heterostyled, 
I  cannot  conjecture.  Some  families  of  considerable 
size,  such  as  the  Boraginese  and  Verbenaceae,  include, 
as  far  as  is  at  present  known,  only  a  single  heterostyled 
genus.  Polygonum  also  is  the  sole  heterostyled  genus 
in  its  family;  and  though  it  is  a  very  large  genus, 
no  other  species  except  P.  fagopyrum  is  thus  charac- 
terised. We  may  suspect  that  it  has  become  hetero- 
styled within  a  comparatively  recent  period,  as  it 
seems  to  be  less  strongly  so  in  function  than  the  species 
in  any  other  genus,  for  both  forms  are  capable  of  yield- 
ing a  considerable  number  of  spontaneously  self-ferti- 
lised seeds.  Polygonum  in  possessing  only  a  single  het- 
erostyled species  is  an  extreme  case;  but  every  other 
genus  of  considerable  size  which  includes  some  such 
species  likewise  contains  homostyled  species.  Lyth- 
rum  includes  trimorphic,  dimorphic,  and  homostyled 
species. 


258  CONCLUDING  REMARKS  CHAP.  VI. 

Trees,  bushes,  and  herbaceous  plants,  both  large 
and  small,  bearing  single  flowers  or  flowers  in  dense 
spikes  or  heads,  have  been  rendered  heterostyled.  So 
have  plants  which  inhabit  alpine  and  lowland  sites,  dry 
land,  marshes  and  water.* 

When  I  first  began  to  experimentise  on  hetero- 
styled plants  it  was  under  the  impression  that  they 
were  tending  to  become  dioecious ;  but  I  was  soon  forced 
to  relinquish  this  notion,  as  the  long-styled  plants 
of  Primula  which,  from  possessing  a  longer  pistil,  larger 
stigma,  shorter  stamens  with  smaller  pollen-grains, 
seemed  to  be  the  more  feminine  of  the  two  forms, 
yielded  fewer  seeds  than  the  short-styled  plants  which 
appeared  to  be  in  the  above  respects  the  more  mascu- 
line of  the  two.  Moreover,  trimorphic  plants  evident- 
ly come  under  the  same  category  with  dimorphic,  and 
the  former  cannot  be  looked  at  as  tending  to  become 
dioecious.  With  Lythrum  salicaria,  however,  we  have 
the  curious  and  unique  case  of  the  mid-styled  form 
being  more  feminine  or  less  masculine  in  nature  than 
the  other  two  forms.  This  is  shown  by  the  large 


*  Out  of  the  38  genera  known  contain  species  inhabiting  the 
to  include  heterostyled  species,  just-specified  stations.  So  that  43 
about  eight,  or  21  per  cent.,  are  per  cent,  of  those  British  plants 
more  or  less  aquatic  in  their  which  have  their  sexes  separated 
habits.  I  was  at  first  struck  with  are  more  or  less  aquatic  in  their 
this  fact,  for  I  was  not  then  aware  habits,  whereas  only  21  per  cent, 
how  large  a  proportion  of  ordinary  of  heterostyled  plants  have  such 
plants  inhabit  such  stations.  Het-  habits.  I  may  add  that  the  her- 
erostyled  plants  may  be  said  in  maphrodite  classes,  from  Monan- 
one  sense  to  have  their  sexes  sepa-  dria  to  Gynandria  inclusive,  con- 
rated,  as  the  forms  must  mutually  tain  447  genera,  of  which  113  are 
fertilise  one  another.  Therefore  aquatic  in  the  above  sense,  or  only 
it  seemed  worth  while  to  ascertain  25  per  cent.  It  thus  appears,  as 
what  proportion  of  the  genera  in  far  as  can  be  judged  from  such 
the  Linnean  classes  Monoecia,  imperfect  data,  that  there  is  some 
Dicecia  and  Polygamia,  contained  connection  between  the  separation 
species  which  live  "in  water,  of  the  sexes  in  plants  and  the 
marshes,  bogs  or  watery  places."  watery  nature  of  the  sites  which 
In  Sir  W.  J.  Hooker's  '  British  they  inhabit ;  but  that  this  does 
Flora '  (4th  edit.  1838")  these  three  not  hold  good  with  heterostyled 
Linnean  classes  include  40  genera,  species. 
17  of  which  (i.e.  43  per  cent.) 


CHAP.  VI.        ON  HETEROSTYLED  PLANTS.  259 

number  of  seeds  which  it  yields  in  whatever  manner 
it  may  be  fertilised,  and  by  its  pollen  (the  grains  of 
which  are  of  smaller  size  than  those  from  the  cor- 
responding stamens  in  the  other  two  forms)  when 
applied  to  the  stigma  of  any  form  producing  fewer 
seeds  than  the  normal  number.  If  we  suppose  the 
process  of  deterioration  of  the  male  organs  in  the  mid- 
styled  form  to  continue,  the  final  result  would  be  the 
production  of  a  female  plant;  and  Lythrum  salicaria 
would  then  consist  of  two  heterostyled  hermaphrodites 
and  a  female.  No  such  case  is  known  to  exist,  but  it 
is  a  possible  one,  as  hermaphrodite  and  female  forms 
of  the  same  species  are  by  no  means  rare.  Although 
there  is  no  reason  to  believe  that  heterostyled  plants 
are  regularly  becoming  dioecious,  yet  they  offer  sin- 
gular facilities,  as  will  hereafter  be  shown,  for  such 
conversion;  and  this  appears  occasionally  to  have  been 
effected. 

We  may  feel  sure  that  plants  have  been  rendered 
heterostyled  to  ensure  cross-fertilisation,  for  we  now 
know  that  a  cross  between  the  distinct  individuals  of 
the  same  species  is  highly  important  for  the  vigour  and 
fertility  of  the  offspring.  The  same  end  is  gained  by 
dichogamy  or  the  maturation  of  the  reproductive  ele- 
ments of  the  same  flower  at  different  periods, — by 
diceciousness — self-sterility — the  prepotency  of  pollen 
from  another  individual  over  a  plant's  own  pollen, — and 
lastly,  by  the  structure  of  the  flower  in  relation  to  the 
visits  of  insects.  The  wonderful  diversity  of  the  means 
for  gaining  the  same  end  in  this  case,  and  in  many 
others,  depends  on  the  nature  of  all  the  previous 
changes  through  which  the  species  had  passed,  and  on 
the  more  or  less  complete  inheritance  of  the  successive 
adaptations  of  each  part  to  the  surrounding  conditions. 
Plants  which  are  already  well  adapted  by  the  structure 


260  CONCLUDING  REMARKS  CHAP.  VI. 

of  their  flowers  for  cross-fertilisation  by  the  aid  of  in- 
sects often  possess  an  irregular  corolla,  which  has  been 
modelled  in  relation  to  their  visits;  and  it  would  have 
been  of  little  or  no  use  to  such  plants  to  have  become 
heterostyled.  We  can  thus  understand  why  it  is  that 
not  a  single  species  is  heterostyled  in  such  great  families 
as  the  Leguminosse,  Labiatse,  Scrophulariaceas,  Orchideae, 
&c.,  all  of  which  have  irregular  flowers.  Every  known 
heterostyled  plant,  however,  depends  on  insects  for  its 
fertilisation,  and  not  on  the  wind ;  so  that  it  is  a  rather 
surprising  fact  that  only  one  genus,  Pontederia,  has  a 
plainly  irregular  corolla. 

Why  some  species  are  adapted  for  cross-fertilisation, 
whilst  others  within  the  same  genus  are  not  so,  or 
if  they  once  were,  have  since  lost  such  adaptation 
and  in  consequence  are  now  usually  self-fertilised,  I 
have  endeavoured  elsewhere  to  explain  to  a  certain 
limited  extent.*  If  it  be  further  asked  why  some 
species  have  been  adapted  for  this  end  by  being  made 
heterostyled,  rather  than  by  any  of  the  above  specified 
means,  the  answer  probably  lies  in  the  manner  in 
which  heterostylism  originated, — a  subject  immedi- 
ately to  be  discussed.  Heterostyled  species,  however, 
have  an  advantage  over  dichogamous  species,  as  all 
the  flowers  on  the  same  heterostyled  plant  belong  to 
the  same  form,  so  that  when  fertilised  legitimately  by 
insects  two  distinct  individuals  are  sure  to  intercross. 
On  the  other  hand,  with  dichogamous  plants,  early  or 
late  flowers  on  the  same  individual  may  intercross; 
and  a  cross  of  this  kind  does  hardly  any  or  no  good. 
Whenever  it  is  profitable  to  a  species  to  produce  a  large 
number  of  seeds,  and  this  obviously  is  a  very  common 
case,  heterostyled  will  have  an  advantage  over  dioecious 
plants,  as  all  the  individuals  of  the  former,  whilst 

*  '  The  Effects  of  Cross  and  Self-fertilisation,'  1876,  p.  441. 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  261 

only  half  of  the  latter,  that  is  the  females,  yield 
seeds.  On  the  other  hand,  heterostyled  plants  seem  to 
have  no  advantage,  as  far  as  cross-fertilisation  is  con- 
cerned, over  those  which  are  sterile  with  their  own  pol- 
len. They  lie  indeed  under  a  slight  disadvantage,  for 
if  two  self-sterile  plants  grow  near  together  and  far 
removed  from  all  other  plants  of  the  same  species,  they 
will  mutually  and  perfectly  'fertilise  one  another, 
whilst  this  will  not  he  the  case  with  heterostyled  di- 
morphic plants,  unless  they  chance  to  belong  to  opposite 
forms. 

It  may  be  added  that  species  which  are  trimorphic 
have  one  slight  advantage  over  the  dimorphic;  for  if 
only  two  individuals  of  a  dimorphic  species  happen  to 
grow  near  together  in  an  isolated  spot,  the  chances  are 
even  that  both  will  belong  to  the  same  form,  and  in 
this  case  they  will  not  produce  the  full  number  of  vigor- 
ous and  fertile  seedlings;  all  these,  moreover,  will  tend 
strongly  to  belong  to  the  same  form  as  their  parents. 
On  the  other  hand,  if  two  plants  of  the  same  trimorphic 
species  happen  to  grow  in  an  isolated  spot,  the  chances 
are  two  to  one  in  favour  of  their  not  belonging  to  the 
same  form;  and  in  this  case  they  will  legitimately  fer- 
tilise one  another,  and  yield  the  full  complement  of  vig- 
orous offspring. 

The  Means  by  which  Plants  may  have  been  rendered 

Heterostyled. 

This  is  a  very  obscure  subject,  on  which  I  can  throw 
little  light,  but  which  is  worthy  of  discussion.  It  has 
been  shown  that  heterostyled  plants  occur  in  fourteen 
natural  families,  dispersed  throughout  the  whole  vege- 
table kingdom,  and  that  even  within  the  family  of  the 
Rubiaceae  they  are  dispersed  in  eight  of  the  tribes.  "We 
may  therefore  conclude  that  this  structure  has  been  ac- 


262  CONCLUDING  REMARKS  CHAP.  VI. 

quired  by  various  plants  independently  of  inheritance 
from  a  common  progenitor,  and  that  it  can  be  acquired 
without  any  great  difficulty — that  is,  without  any  very 
unusual  combination  of  circumstances. 

It  is  probable  that  the  first  step  towards  a  species 
becoming  heterostyled  is  great  variability  in  the  length 
of  the  pistil  and  stamens,  or  of  the  pistil  alone.  Such 
variations  are  not  very  rare:  with  Amsinckia  specta- 
~bilis  and  Nolana  prostrata  these  organs  differ  so  much 
in  length  in  different  individuals  that  until  experiment- 
ing on  them,  I  thought  both  species  heterostyled.  The 
stigma  of  Gesneria  pendulina  sometimes  protrudes  far 
beyond,  and  is  sometimes  seated  beneath  the  anthers; 
so  it  is  with  Oxalis  acetosella  and  various  other  plants. 
I  have  also  noticed  an  extraordinary  amount  of  differ- 
ence in  the  length  of  the  pistil  in  cultivated  varieties  of 
Primula  veris  and  vulgaris. 

As  most  plants  are  at  least  occasionally  cross-fer- 
tilised by  the  aid  of  insects,  we  may  assume  that  this 
was  the  case  with  our  supposed  varying  plant;  but 
that  it  would  have  been  beneficial  to  it  to  have  been 
more  regularly  cross-fertilised.  We  should  bear  in 
mind  how  important  an  advantage  it  has  been  proved 
to  be  to  many  plants,  though  in  different  degrees  and 
ways,  to  be  cross-fertilised.  It  might  well  happen  that 
our  supposed  species  did  not  vary  in  function  in  the 
right  manner,  so  as  to  become  either  dichogamous  or 
completely  self-sterile,  or  in  structure  so  as  to  ensure 
cross-fertilisation.  If  it  had  thus  varied,  it  would  never 
have  been  rendered  heterostyled,  as  this  state  would 
then  have  been  superfluous.  But  the  parent-species  of 
our  several  existing  heterostyled  plants  may  have  been, 
and  probably  were  (judging  from  their  present  consti- 
tution) in  some  degree  self-sterile ;  and  this  would  have 
made  regular  cross-fertilisation  still  more  desirable. 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  263 

Now  let  us  take  a  highly  varying  species  with  most 
or  all  of  the  anthers  exserted  in  some  individuals,  and 
in  others  seated  low  down  in  the  corolla;  with  the 
stigma  also  varying  in  position  in  like  manner.  Insects 
which  visited  such  flowers  would  have  different  parts 
of  their  bodies  dusted  with  pollen,  and  it  would  be  a 
mere  chance  whether  this  were  left  on  the  stigma  of 
the  next  flower  which  was  visited.  If  all  the  anthers 
could  have  been  placed  on  the  same  level  in  all  the 
plants,  then  abundant  pollen  would  have  adhered  to 
the  same  part  of  the  body  of  the  insects  which  fre- 
quented the  flowers,  and  would  afterwards  have  been 
deposited  without  loss  on  the  stigma,  if  it  likewise 
stood  on  the  same  unvarying  level  in  all  the  flowers. 
But  as  the  stamens  and  pistils  are  supposed  to  have 
already  varied  much  in  length  and  to  be  still  varying, 
it  might  well  happen  that  they  could  be  reduced  much 
more  easily  through  natural  selection  into  two  sets  of 
different  lengths  in  different  individuals,  than  all  to  the 
same  length  and  level  in  all  the  individuals.  We  know 
from  innumerable  instances,  in  which  the  two  sexes  and 
the  young  of  the  same  species  differ,  that  there  is  no 
difficulty  in  two  or  more  sets  of  individuals  being  formed 
which  inherit  different  characters.  In  our  particular 
case  the  law  of  compensation  or  balancement  (which 
is  admitted  by  many  botanists)  would  tend  to  cause  the 
pistil  to  be  reduced  in  those  individuals  in  which  the 
stamens  were  greatly  developed  and  to  be  increased  in 
length  in  those  which  had  their  stamens  but  little  de- 
veloped. 

Now  if  in  our  varying  species  the  longer  stamens 
were  to  be  nearly  equalised  in  length  in  a  considerable 
body  of  individuals,  with  the  pistil  more  or  less  reduced ; 
and  in  another  body,  the  shorter  stamens  to  be  simi- 
larly equalised,  with  the  pistil  more  or  less  increased  in 


264  CONCLUDING  REMARKS  CHAP.  VI. 

length,  cross-fertilisation  would  be  secured  with  little 
loss  of  pollen;  and  this  change  would  be  so  highly 
beneficial  to  the  species,  that  there  is  no  difficulty  in  be- 
lieving that  it  could  be  effected  through  natural  selec- 
tion. Our  plant  would  then  make  a  close  approach  in 
structure  to  a  heterostyled  dimorphic  species;  or  to  a 
trimorphic  species,  if  the  stamens  were  reduced  to  two 
lengths  in  the  same  flower  in  correspondence  with  that 
of  the  pistils  in  the  other  two  forms.  But  we  have  not 
as  yet  even  touched  on  the  chief  difficulty  in  under- 
standing how  heterostyled  species  could  have  originated. 
A  completely  self-sterile  plant  or  a  dichogamous  one  can 
fertilise  and  be  fertilised  by  any  other  individual  of  the 
same  species;  whereas  the  essential  character  of  a 
heterostyled  plant  is  that  an  individual  of  one  form  can- 
not fully  fertilise  or  be  fertilised  by  an  individual  of 
the  same  form,  but  only  by  one  belonging  to  another 
form. 

H.  Miiller  has  suggested  *  that  ordinary  or  homo- 
styled  plants  may  have  been  rendered  heterostyled 
merely  through  the  effects  of  habit.  Whenever  pollen 
from  one  set  of  anthers  is  habitually  applied  to  a  pistil 
of  particular  length  in  a  varying  species,  he  believes 
that  at  last  the  possibility  of  fertilisation  in  any  other 
manner  will  be  nearly  or  completely  lost.  He  was  led 
to  this  view  by  observing  that  Diptera  frequently  car- 
ried pollen  from  the  long-styled  flowers  of  Hottonia  to 
the  stigma  of  the  same  form,  and  that  this  illegitimate 
union  was  not  nearly  so  sterile  as  the  corresponding 
union  in  other  heterostyled  species.  But  this  conclu- 
sion is  directly  opposed  by  some  other  cases,  for  instance 
by  that  of  Linum  grandiflorum ;  for  here  the  long- 
styled  form  is  utterly  barren  with  its  own-form  pollen, 
although  from  the  position  of  the  anthers  this  pollen 

*  '  Die  Befruchtung  der  Blumen,'  p.  352. 


CHAP.  VI.         OX  HETEROSTYLED  PLANTS.  265 

is  invariably  applied  to  the  stigma.  It  is  obvious  that 
with  heterostyled  dimorphic  plants  the  two  female 
and  the  two  male  organs  differ  in  power;  for  if  the 
same  kind  of  pollen  be  placed  on  the  stigmas  of  the 
two  forms,  and  again  if  the  two  kinds  of  pollen  be  placed 
on  the  stigmas  of  the  same  form,  the  results  are  in 
each  case  widely  different.  Nor  can  we  see  how  this 
differentiation  of  the  two  female  and  two  male  organs 
could  have  been  effected  merely  through  each  kind 
of  pollen  being  habitually  placed  on  one  of  the  two 
stigmas. 

Another  view  seems  at  first  sight  probable,  namely, 
that  an  incapacity  to  be  fertilised  in  certain  ways  has 
been  specially  acquired  by  heterostyled  plants.  We 
may  suppose  that  our  varying  species  was  somewhat 
sterile  (as  is  often  the  case)  with  pollen  from  its  own 
stamens,  whether  these  were  long  or  short:  and  that 
such  sterility  was  transferred  to  all  the  individuals 
with  pistils  and  stamens  of  the  same  length,  so  that 
these  became  incapable  of  intercrossing  freely;  but 
that  such  sterility  was  eliminated  in  the  case  of  the 
individuals  which  differed  in  the  length  of  their  pistils 
and  stamens.  It  is,  however,  incredible  that  so  peculiar 
a  form  of  mutual  infertility  should  have  been  specially 
acquired  unless  it  were  highly  beneficial  to  the  species; 
and  although  it  may  be  beneficial  to  an  individual 
plant  to  be  sterile  with  its  own  pollen,  cross-fertilisa- 
tion being  thus  ensured,  how  can  it  be  any  advan- 
tage to  a  plant  to  be  sterile  with  half  its  brethren, 
that  is,  with  all  the  individuals  belonging  to  the  same 
form?  Moreover,  if  the  sterility  of  the  unions  between 
plants  of  the  same  form  had  been  a  special  acquire- 
ment, we  might  have  expected  that  the  long-styled  form 
fertilised  by  the  long-styled  would  have  been  sterile 
in  the  same  degree  as  the  short-styled  fertilised  by 
19 


266  CONCLUDING  REMARKS  CHAP.  VI. 

the  short-styled;  but  this  is  hardly  ever  the  case.  On 
the  contrary,  there  is  sometimes  the  widest  differ- 
ence in  this  respect,  as  between  the  two  illegitimate 
unions  of  Pulmonaria  angustifolia  and  of  Hottonia  pa- 
lustris. 

It  is  a  more  probable  view  that  the  male  and  female 
organs  in  two  sets  of  individuals  have  been  by  some 
means  specially  adapted  for  reciprocal  action;  and 
that  the  sterility  between  the  individuals  of  the  same 
set  or  form  is  an  incidental  and  purposeless  result. 
The  meaning  of  the  term  "  incidental ''  may  be  illus- 
trated by  the  greater  or  less  difficulty  in  grafting  or 
budding  together  two  plants  belonging  to  distinct 
species;  for  as  this  capacity  is  quite  immaterial  to 
the  welfare  of  either,  it  cannot  have  been  specially 
acquired,  and  must  be  the  incidental  result  of  differ- 
ences in  their  vegetative  systems.  But  how  the  sex- 
ual elements  of  heterostyled  plants  came  to  differ  from 
what  they  were  whilst  the  species  was  homostyled, 
and  how  they  became  co-adapted  in  two  sets  of  indi- 
viduals, are  very  obscure  points.  We  know  that  in 
the  two  forms  of  our  existing  heterostyled  plants  the 
pistil  always  differs,  and  the  stamens  generally  differ 
in  length;  so  does  the  stigma  in  structure,  the  anthers 
in  size,  and  the  pollen-grains  in  diameter.  It  ap- 
pears, therefore,  at  first  sight  probable  that  organs 
which  differ  in  such  important  respects  could  act  on 
one  another  only  in  some  manner  for  which  they  had 
been  specially  adapted.  The  probability  of  this  view 
is  supported  by  the  curious  rule  that  the  greater 
the  difference  in  length  between  the  pistils  and  sta- 
mens of  the  trimorphic  species  of  Lythrum  and  Oxalis, 
the  products  of  which  are  united  for  reproduction,  by 
so  much  the  greater  is  the  infertility  of  the  union. 
The  same  rule  applies  to  the  two  illegitimate  unions 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  267 

of  some  dimorphic  species,  namely,  Primula  vulgaris 
and  Pulmonaria  angustifolia;  but  it  entirely  fails  in 
other  cases,  as  with  Hottonia  palustris  and  Linum 
grandiflorum.  We  shall,  however,  best  perceive  the  diffi- 
culty of  understanding  the  nature  and  origin  of  the 
co-adaptation  between  the  reproductive  organs  of  the 
two  forms  of  heterostyled  plants,  by  considering  the  case 
of  Linum  grandiflorum:  the  two  forms  of  this  plant 
differ  exclusively,  as  far  as  we  can  see,  in  the  length 
of  their  pistils ;  in  the  long-styled  form,  the  ^stamens 
equal  the  pistil  in  length,  but  their  pollen  has  no  more 
effect  on  it  than  so  much  inorganic  dust;  whilst  this 
pollen  fully  fertilises  the  short  pistil  of  the  other  form. 
Now,  it  is  scarcely  credible  that  a  mere  difference 
in  the  length  of  the  pistil  can  make  a  wide  difference 
in  its  capacity  for  being  fertilised.  We  can  believe  this 
the  less  because  with  some  plants,  for  instance,  Am- 
sinckia  spectabilis,  the  pistil  varies  greatly  in  length 
without  affecting  the  fertility  of  the  individuals  which 
are  intercrossed.  So  again  I  observed  that  the  same 
plants  of  Primula  veris  and  vulgaris  differed  to  an  ex- 
traordinary degree  in  the  length  of  their  pistils  during 
successive  seasons;  nevertheless  they  yielded  during 
these  seasons  exactly  the  same  average  number  of  seeds 
when  left  to  fertilise  themselves  spontaneously  under  a 
net. 

We  must  therefore  look  to  the  appearance  of  inner 
or  hidden  constitutional  differences  between  the  indi- 
viduals of  a  varying  species,  of  such  a  nature  that  the 
male  element  of  one  set  is  enabled  to  act  efficiently 
only  on  the  female  element  of  another  set.  We  need 
not  doubt  about  the  possibility  of  variations  in  the 
constitution  of  the  reproductive  system  of  a  plant,  for 
we  know  that  some  species  vary  so  as  to  be  completely 
self -sterile  or  completely  self -fertile,  either  in  an  appar- 


268  CONCLUDING  REMARKS  CHAP.  VI. 

ently  spontaneous  manner  or  from  slightly  changed 
conditions  of  life.  Gartner  also  has  shown  *  that  the  in- 
dividual plants  of  the  same  species  vary  in  their  sexual 
powers  in  such  a  manner  that  one  will  unite  with  a 
distinct  species  much  more  readily  than  another.  But 
what  the  nature  of  the  inner  constitutional  differences 
may  be  between  the  sets  or  forms  of  the  same  varying 
species,  or  between  distinct  species,  is  quite  unknown. 
It  seems  therefore  probable  that  the  species  which 
have  become  heterostyled  at  first  varied  so  that  two 
or  three  sets  of  individuals  were  formed  differing  in 
the  length  of  their  pistils  and  stamens  and  in  other 
co-adapted  characters,  and  that  almost  simultaneously 
the  irreproductive  powers  became  modified  in  such  a 
manner  that  the  sexual  elements  in  one  set  were 
adapted  to  act  on  the  sexual  elements  of  another  set; 
and  consequently  that  these  elements  in  the  same  set 
or  form  incidentally  became  ill-adapted  for  mutual 
interaction,  as  in  the  case  of  distinct  species.  I  have 
elsewhere  shown  f  that  the  sterility  of  species  when 
first  crossed  and  of  their  hybrid  offspring  must  also  be 
looked  at  as  merely  an  incidental  result,  following  from 
the  special  co-adaptation  of  the  sexual  elements  of  the 
same  species.  We  can  thus  understand  the  striking 
parallelism,  which  has  been  shown  to  exist  between  the 
effects  of  illegitimately  uniting  heterostyled  plants  and 
of  crossing  distinct  species.  The  great  difference  in  the 
degree  of  sterility  between  the  various  heterostyled  spe- 


*  Gartner,      '  Bastarderzeugung  act  on  the  reproductive  system  of 

im  Pflanzenreich,'  1849,  p.  165.  most  organisms,  it  is  probable  that 

t  '  Origin  of  Species,'  6th  edit,  the  close  adaptation  of  the  male  to 
p.  247  ;  '  Variation  of  Animals  and  the  female  elements  in  the  two 
Plants  under  Domestication.'  2nd  forms  of  the  same  heterostyled 
edit.  vol.  ii.  p.  169 ;  '  The  Effects  species,  or  in  all  the  individuals 
of  Cross-  and  Self-fertilisation,'  p.  of  the  same  ordinary  species,  could 
463.  It  may  be  well  here  to  re-  be  acquired  only  under  long-con- 
mark  that,  judging  from  the  re-  tinued  nearly  uniform  conditions 
markable  power  with  which  ab-  of  life, 
ruptly  changed  conditions  of  life 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  £69 

cies  when  illegitimately  fertilised,  and  between  the  two 
forms  of  the  same  species  when  similarly  fertilised,  har- 
monises well  with  the  view  that  the  result  is  an  inci- 
dental one  which  follows  from  changes  gradually  effected 
in  their  reproductive  systems,  in  order  that  the  sexual 
elements  of  the  distinct  forms  should  act  perfectly  on 
one  another. 

Transmission  of  the  Two  Forms  by  Heterostyled 
'Plants. — The  transmission  of  the  two  forms  by  hetero- 
styled  plants,  with  respect  to  which  many  facts  were 
given  in  the  last  chapter,  may  perhaps  be  found  here- 
after to  throw  some  light  on  their  manner  of  develop- 
ment. Hildebrand  observed  that  seedlings  from  the 
long-styled  form  of  Primula  Sinensis  when  fertilised 
with  pollen  from  the  same  form  were  mostly  long-styled, 
and  many  analogous  cases  have  since  been  observed  by 
me.  All  the  known  cases  are  given  in  the  two  follow- 
ing tables  (3G  and  37). 

We  see  in  these  two  tables  that  the  offspring  from 
a  form  illegitimately  fertilised  with  pollen  from 
another  plant  of  the  same  form  belong,  with  a  few 
exceptions,  to  the  same  form  as  their  parents.  For 
instance,  out  of  162  seedlings  from  long-styled  plants 
of  Primula  veris  fertilised  during  five  generations  in 
this  manner,  156  were  long-styled  and  only  6  short- 
styled.  Of  69  seedlings  from  P.  vulgaris  similarly 
raised  all  were  long-styled.  So  it  was  with  56  seedlings 
from  the  long-styled  form  of  the  trimorphic  Lythrum 
salicaria,  and  with  numerous  seedlings  from  the  long- 
styled  form  of  Oxalis  rosea.  The  offspring  from  the 
short-styled  forms  of  dimorphic  plants,  and  from  both 
the  mid-styled  and  short-styled  forms  of  trimorphic 
plants,  fertilised  with  their  own-form  pollen,  likewise 
tend  to  belong  to  the  same  form  as  their  parents,  but 


270 


CONCLUDING  REMARKS 


CHAP.  VI. 


TABLE  36. 

Nature  of  the  Offspring  from  Illegitimately  fertilised 
Dimorphic  Plants. 


Numberl  Number 
of  LOUR- of  Short- 

«tyle.l    i    styled 
Offspring  Offering 


Primula  veris     .    ,    . 


Primula  vulgaris 


Primula  auricula    .    . 


Primula  Sinensis    . 


Long-styled  form,  fertilised  by 
own-form  pollen  during  five 
successive  generations,  pro- 
duced   

'Short-styled  form,  fertilised) 
by  own-form  pollen,  pro-  \ 
duced J 

Long-styled  form,  fertilised  by  1 
own-form  pollen  during  two  I 
successive  generations,  pro-  ( 
duced J 

Short-styled  form,  fertilised 
by  own-form  pollen,  is  said 
to  produce  during  successive 
generations  offspring  in 
about  the  following  propor- 
tions .  . 


Pulmonaria  officinalis 
Polygonum  fagopyrum 


Long-styled  form,  fertilised  by "] 
own-form  pollen  during  two  I 
successive  generations,  pro-  [ 
duced J 

f  Long-styled  form,  fertilised  by  ) 
•<  own-form  pollen  (Hilde-  f 
(.  brand),  produced  .  .  .  .  J 

f Short-styled  form,  fertilised) 
«  by  own  form  pollen,  pro-  > 
(  duced J 

f  Long-styled  form,  fertilised  by  ) 
{  own-form  pollen,  produced .  j 

f  Long-styled  form,  fertilised  by  ) 
1  own-form  pollen,  produced  .  J 

(Short-styled  form,  fertilised) 
-j  by  own-form  pollen,  pro-  > 
<  duced J 


CHAP.  VI.         ON  HETEEOSTYLED  PLANTS. 


271 


TABLE  37. 

Nature  of  the  Offspring  from  Illegitimately  fertilised 
Trimorphic  Plants. 


— 

Number 

°» 
Oflspring 

Numbei 
of  Mid- 

<3£ 

Number 
|of  Short- 
j    8tyled 
Offspring 

f  Long-styled  form,  fertilised  ) 
Lythrumsalicaria.  1     by  own-form  pollen,  pro-  \ 
(     duced     J 

f  Short-styled  form,  fertilised  ) 
•j      by  own-form  pollen,  pro-  V 
(     duced    J 

56 
1 

0 
0 

0 

8 

{Short-styled  form,  fertilised  1 
by  pollen  from  mid-length  1 
stamens    of  long  -styled  | 
form,  produced  .     .     .     .  J  ' 

("Mid-styled  form,  fertilised) 
<      by  own-form  pollen,  pro-  > 
(_     duced                                   J 

4 
1 

0 
3 

8 
0 

f  Mid-styled  form,  fertilised] 
«              .<         I      by  pollen  from  shortest  i 
1      stamens    of    long-styled  [ 
[     form,  produced    .     .     .     J 

f  Mid-styled  form,  fertilised] 
«              <t         I      by  pollen    from    longest  1 
1      stamens    of    short-styled  f 
[     form,  produced  .     .     .     .  J 

f  Long-styled  form,  fertilised 
during    several    genera- 
Oxalis  rosea  .     .     .  i      tions  by  own-form  pollen, 
produced  offspring  in  the 
[     ratio  of  

17 
14 

100 

8 
8 

0 

0 

18 

0 

(Mid-styled  form,  fertilised) 
"  hedysaroides  <      by  own-form  pollen,  pro-  > 
(     duced    J 

0 

17 

0 

not  in  so  marked  a  manner  as  in  the  case  of  the  long- 
styled  form.  There  are  three  cases  in  Table  37,  in 
which  a  form  of  Lythrum  was  fertilised  illegitimately 
with  pollen  from  another  form;  and  in  two  of  these 
cases  all  the  offspring  belonged  to  the  same  two  forms 


272  CONCLUDING  REMARKS  CHAP.  VI. 

as  their  parents,  whilst  in  the  third  case  they  belonged 
to  all  three  forms. 

The  cases  hitherto  given  relate  to  illegitimate  unions, 
but  Hildebrand,  Fritz  Miiller,  and  myself  found  that 
a  very  large  proportion,  or  all  of  the  offspring,  from  a 
legitimate  union  between  any  two  forms  of  the  tri- 
morphic  species  of  Oxalis  belonged  to  the  same  two 
forms.  A  similar  rule  therefore  holds  good  with  unions 
which  are  fully  fertile,  as  with  those  of  an  illegiti- 
mate nature  which  are  more  or  less  sterile.  When 
some  of  the  seedlings  from  a  heterostyled  plant  belong 
to  a  different  form  from  that  of  its  parents,  Hildebrand 
accounts  for  the  fact  by  reversion.  For  instance,  the 
long-styled  parent-plant,  of  Primula  veris,  from  which 
the  162  illegitimate  seedlings  in  Table  36  were  derived 
in  the  course  of  five  generations,  was  itself  no  doubt 
derived  from  the  union  of  a  long-styled  and  a  short- 
styled  parent;  and  the  6  short-styled  seedlings  may  be 
attributed  to  reversion  to  their  short-styled  progenitor. 
But  it  is  a  surprising  fact  in  this  case,  and  in  other 
similar  ones,  that  the  number  of  the  offspring  which 
thus  reverted  was  not  larger.  The  fact  is  rendered  still 
more  strange  in  the  particular  instance  of  P.  veris,  for 
there  was  no  reversion  until  four  or  five  generations  of 
long-styled  plants  had  been  raised.  It  may  be  seen  in 
both  tables  that  the  long-styled  form  transmits  its  form 
much  more  faithfully  than  does  the  short-styled,  when 
both  are  fertilised  with  their  own-form  pollen ;  and  why 
this  should  be  so  it  is  difficult  to  conjecture,  unless  it  be 
that  the  aboriginal  parent-form  of  most  heterostyled 
species  possessed  a  pistil  which  exceeded  its  own  stamens 
considerably  in  length.*  I  will  only  add  that  in  a  state 


*  It  may  be  suspected  that  this  Scott,   'Journal  Linn.  Soc.   Bot.,' 

was  the  case  with  Primula,  judg-  vol.  viii.,  1864,  p.  85).   HerrBreit- 

ing  from  the  length  of  the  pistil  in  enbach  found  many  specimens  of 

geveral  allied  genera  (see  Mr.  J.  Primula  elatior  growing  in  a  state 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  373 

of  nature  any  single  plant  of  a  trimorphic  species  no 
doubt  produces  all  three  forms ;  and  this  may  be  ac- 
counted for  either  by  its  several  flowers  being  sepa- 
rately fertilised  by  both  the  other  forms,  as  Hildebrand 
supposes;  or  by  pollen  from  both  the  other  forms 
being  deposited  by  insects  on  the  stigma  of  the  same 
flower. 

Equal-styled  varieties. — The  tendency  of  the  di- 
morphic species  of  Primula  to  produce  equal-styled 
varieties  deserves  notice.  Cases  of  this  kind  have 
been  observed,  as  shown  in  the  last  chapter,  in  no  less 
than  six  species,  namely,  P.  veris,  vulgaris,  Sinensis, 
auricula,  farinosa,  and  elatior.  In  the  case  of  P.  veris, 
the  stamens  resemble  in  length,  position  and  size 
of  their  pollen-grains  the  stamens  of  the  short-styled 
form;  whilst  the  pistil  closely  resembles  that  of  the 
long-styled,  but  as  it  varies  much  in  length,  one  proper 
to  the  short-styled  form  appears  to  have  been  elongated 
and  to  have  assumed  at  the  same  time  the  functions 
of  a  long-styled  pistil.  Consequently  the  flowers  are 
capable  of  spontaneous  self-fertilisation  of  a  legiti- 
mate nature  and  yield  a  full  complement  of  seed,  or 
even  more  than  the  number  produced  by  ordinary 
flowers  legitimately  fertilised.  With  P.  Sinensis,  on 
the  other  hand,  the  stamens  resemble  in  all  respects 
the  shorter  ones  proper  to  the  long-styled  form,  whilst 
the  pistil  makes  a  near  approach  to  that  of  the  short- 
styled,  but  as  it  varies  in  length,  it  would  appear  as 
if  a  long-styled  pistil  had  been  reduced  in  length  and 
modified  in  function.  The  flowers  in  this  case  as  in 
the  last  are  capable  of  spontaneous  legitimate  ferti- 
lisation, and  are  rather  more  productive  than  ordinary 


of  nature  with  some  flowers  on  the  greatly  preponderated  in  number; 

same    plant     long-styled,     others  there  being  61  of  this  form  to  9 

short-styled     and    others    equal-  of  the  short-styled  and  15  of  the 

styled ;  and  the  long-styled  form  equal-styled. 


274  CONCLUDING  REMARKS  CHAP.  VL 

flowers  legitimately  fertilised.  With  P.  auricula  and 
farinosa  the  stamens  resemble  those  of  the  short-styled 
form  in  length,  but  those  of  the  long-styled  in  the 
size  of  their  pollen-grains ;  the  pistil  also  resembles  that 
of  the  long-styled,  so  that  although  the  stamens  and 
pistil  are  of  nearly  equal  length,  and  consequently 
pollen  is  spontaneously  deposited  on  the  stigma,  yet 
the  flowers  are  not  legitimately  fertilised  and  yield 
only  a  very  moderate  supply  of  seed.  We  thus  see, 
firstly,  that  equal-styled  varieties  have  originated  in 
various  ways,  and,  secondly,  that  the  combination  of 
the  two  forms  in  the  same  flower  differs  in  complete- 
ness. With  P.  elatior  some  of  the  flowers  on  the  same 
plant  have  become  equal-styled,  instead  of  all  of  them 
as  in  the  other  species. 

Mr.  Scott  has  suggested  that  the  equal-styled  varie- 
ties arise  through  reversion  to  the  former  homostyled 
condition  of  the  genus.  This  view  is  supported  by  the 
remarkable  fidelity  with  which  the  equal-styled  varia- 
tion is  transmitted  after  it  has  once  appeared.  I  have 
shown  in  Chapter  XIII  of  my  "  Variation  of  Animals 
and  Plants  under  Domestication/'  that  any  cause  which 
disturbs  the  constitution  tends  to  induce  reversion,  and 
it  is  chiefly  the  cultivated  species  of  Primula  which  be- 
come equal-styled.  Illegitimate  fertilisation,  which  is 
an  abnormal  process,  is  likewise  an  exciting  cause;  and 
with  illegitimately  descended  long-styled  plants  of  P. 
Sinensis,  I  have  observed  the  first  appearance  and  sub- 
sequent stages  of  this  variation.  With  some  other  plants 
of  P.  Sinensis  of  similar  parentage  the  flowers  ap- 
peared to  have  reverted  to  their  original  wild  con- 
dition. Again,  some  hybrids  between  P.  veris  and 
vulgaris  were  strictly  equal-styled,  and  others  made 
a  near  approach  to  this  structure.  All  these  facts 
support  the  view  that  this  variation  results,  at  least 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  275 

in  part,  from  reversion  to  the  original  state  of  the 
genus,  before  the  species  had  become  heterostyled. 
On  the  other  hand,  some  considerations  indicate,  as 
previously  remarked,  that  the  aboriginal  parent-form 
of  Primula  had  a  pistil  which  exceeded  the  stamens 
in  length.  The  fertility  of  the  equal-styled  varieties 
has  been  somewhat  modified,  being  sometimes  greater 
and  sometimes  less  than  that  of  a  legitimate  union. 
Another  view,  however,  may  be  taken  with  respect 
to  the  origin  of  the  equal-styled  varieties,  and  their 
appearance  may  be  compared  with  that  of  hermaphro- 
dites amongst  animals  which  properly  have  their  sexes 
separated;  for  the  two  sexes  are  combined  in  a  mon- 
strous hermaphrodite  in  a  somewhat  similar  manner 
as  the  two  sexual  forms  are  combined  in  the  same 
flower  of  an  equal-styled  variety  of  a  heterostyled 
species. 

Final  remarks. — The  existence  of  plants  which  have 
been  rendered  heterostyled  is  a  highly  remarkable 
phenomenon,  as  the  two  or  three  forms  of  the  same 
undoubted  species  differ  not  only  in  important  points 
of  structure,  but  in  the  nature  of  their  reproductive 
powers.  As  far  as  structure  is  concerned,  the  two 
sexes  of  many  animals  and  of  some  plants  differ  to  an 
extreme  degree;  and  in  both  kingdoms  the  same 
species  may  consist  of  males,  females,  and  hermaphro- 
dites. Certain  hermaphrodite  cirripedes  are  aided  in 
their  reproduction  by  a  whole  cluster  of  what  I  have 
called  complemental  males,  which  differ  wonderfully 
from  the  ordinary  hermaphrodite  form.  With  ants 
we  have  males  and  females,  and  two  or  three  castes  of 
sterile  females  or  workers.  With  Termites  there  are, 
as  Fritz  Miiller  has  shown,  both  winged  and  wingless 
males  and  females,  besides  the  workers.  But  in  none 


276  CONCLUDIDG  REMARKS  CHAP.  VI. 

of  these  cases  is  there  any  reason  to  believe  that  the 
several  males  or  several  females  of  the  same  species 
differ  in  their  sexual  powers,  except  in  the  atrophied 
condition  of  the  reproductive  organs  in  the  workers 
of  social  insects.  Many  hermaphrodite  animals  must 
unite  for  reproduction,  but  the  necessity  of  such 
union  apparently  depends  solely  on  their  structure. 
On  the  other  hand,  with  heterostyled  dimorphic 
species  there  are  two  females  and  two  sets  of  males, 
and  with  trimorphic  species  three  females  and  three 
sets  of  males,  which  differ  essentially  in  their  sexual 
powers.  We  shall,  perhaps,  best  perceive  the  complex 
and  extraordinary  nature  of  the  marriage  arrangements 
of  a  trimorphic  plant  by  the  following  illustration. 
Let  us  suppose  that  the  individuals  of  the  same  species 
of  ant  always  lived  in  triple  communities;  and  that 
in  one  of  these,  a  large-sized  female  (differing  also  in 
other  characters),  lived  with  six  middle-sized  and  six 
small-sized  males;  in  the  second  community  a  middle- 
sized  female  lived  with  six  large-  and  six  small-sized 
males;  and  in  the  third,  a  small-sized  female  lived 
with  six  large-  and  six  middle-sized  males.  Each  of 
these  three  females,  though  enabled  to  unite  with  any 
male,  would  be  nearly  sterile  with  her  own  two  sets  of 
males,  and  likewise  with  two  other  sets  of  males  of  the 
same  size  with  her  own  which  lived  in  the  other  two 
communities;  but  she  would  be  fully  fertile  when 
paired  with  a  male  of  her  own  size.  Hence  the  thirty- 
six  males,  distributed  by  half-dozens  in  the  three  com- 
munities, would  be  divided  into  three  sets  of  a  dozen 
each;  and  these  sets,  as  well  as  the  three  females, 
would  differ  from  one  another  in  their  reproductive 
powers  in  exactly  the  same  manner  as  do  the  distinct 
species  of  the  same  genus.  But  it  is  a  still  more 
remarkable  fact  that  young  ants  raised  from  any  one 


CHAP.  VI.         ON  HETEROSTYLED  PLANTS.  277 

of  the  three  female  ants,  illegitimately  fertilised  by  a 
male  of  a  different  size,  would  resemble  in  a  whole 
series  of  relations  the  hybrid  offspring  from  a  cross 
between  two  distinct  species  of  ants.  They  would  be 
dwarfed  in  nature,  and  more  or  less,  or  even  utterly 
barren.  Naturalists  are  so  much  accustomed  to  behold 
great  diversities  of  structure  associated  with  the  two 
sexes,  that  they  feel  no  surprise  at  almost  any  amount 
of  difference ;  but  differences  in  sexual  nature  have  been 
thought  to  be  the  very  touchstone  of  specific  distinction. 
We  now  see  that  such  sexual  differences — the  greater  or 
less  power  of  fertilising  and  being  fertilised — may  char- 
acterise the  co-existing  individuals  of  the  same  species, 
in  the  same  manner  as  they  characterise  and  have  kept 
separate  those  groups  of  individuals  produced  during 
the  lapse  of  ages,  which  we  rank  and  denominate  as 
distinct  species. 


278  DICECIOUS  AND  CHAP.  VII. 


CHAPTER  VII. 
POLYGAMOUS,  DICECIOUS,  AND  GYKO-DICECIOUS  PLANTS. 

The  conversion  in  various  ways  of  hermaphrodite  into  dioecious  plants 
— Heterostyled  plants  rendered  dioecious — Rubiacese — Verbenaceae 
— Polygamous  and  sub-dioecious  plants — Euonymus — Fragaria — 
The  two  sub-forms  of  both  sexes  of  Khamnus  and  Epigsea — Ilex — 
Gyno-dicecious  plants — Thymus,  difference  in  fertility  of  the  her- 
maphrodite and  female  individuals — Satureia — Manner  in  which 
the  two  forms  probably  originated — Scabiosa  and  other  gyno-dice- 
cious  plants — Difference  in  the  size  of  the  corolla  in  the  forms  of 
polygamous,  dioecious,  and  gyno-dicecious  plants. 

THERE  are  several  groups  of  plants  in  which  all  the 
species  are  dioecious,  and  these  exhibit  no  rudiments 
in  the  one  sex  of  the  organs  proper  to  the  other. 
About  the  origin  of  such  plants  nothing  is  known.  It 
is  possible  that  they  may  be  descended  from  ancient 
lowly  organized  forms,  which  had  from  the  first  their 
sexes  separated;  so  that  they  have  never  existed  as 
hermaphrodites.  There  are,  however,  many  other 
groups  of  species  and  single  ones,  which  from  being 
allied  on  all  sides  to  hermaphrodites,  and  from  exhib- 
iting in  the  female  flowers  plain  rudiments  of  male 
organs,  and  conversely  in  the  male  flowers  rudiments 
of  female  organs,  we  may  feel  sure  are  descended  from 
plants  which  formerly  had  the  two  sexes  combined  in 
the  same  flower.  It  is  a  curious  and  obscure  problem 
how  and  why  such  hermaphrodites  have  been  rendered 
bisexual. 

If  in  some  individuals  of  a  species  the  stamens 
alone  were  to  abort,  females  and  "hermaphrodites  would 


CHAP.  VII.  POLYGAMOUS  PLANTS.  279 

be  left  existing,  of  which  many  instances  occur;  and  if 
the  female  organs  of  the  hermaphrodite  were  afterwards 
to  abort,  the  result  would  be  a  dioecious  plant.  Con- 
versely, if  we  imagine  the  female  organs  alone  to  abort 
in  some  individuals,  males  and  hermaphrodites  would 
be  left;  and  the  hermaphrodites  might  afterwards  be 
converted  into  females. 

In  other  cases,  as  in  that  of  the  common  Ash-tree 
mentioned  in  the  Introduction,  the  stamens  are  rudimen- 
tary in  some  individuals,  the  pistils  in  others,  others 
again  remaining  as  hermaphrodites.  Here  the  modifi- 
cation of  the  two  sets  of  organs  appears  to  have  occurred 
simultaneously,  as  far  as  we  can  judge  from  their  equal 
state  of  abortion.  If  the  hermaphrodites  were  sup- 
planted by  the  individuals  having  separated  sexes,  and 
if  these  latter  were  equalised  in  number,  a  strictly  dioe- 
cious species  would  be  formed. 

There  is  much  difficulty  in  understanding  why  her- 
maphrodite plants  should  ever  have  been  rendered 
dioecious.  There  would  be  no  such  conversion,  unless 
pollen  was  already  carried  regularly  by  insects  or  by  the 
wind  from  one  individual  to  the  other;  for  otherwise 
every  step  towards  diceciousness  would  lead  towards 
sterility.  As  we  must  assume  that  cross-fertilisation 
was  assured  before  an  hermaphrodite  could  be  changed 
into  a  dioecious  plant,  we  may  conclude  that  the  con- 
version has  not  been  effected  for  the  sake  of  gaining 
the  great  benefits  which  follow  from  cross-fertilisa- 
tion. We  can,  however,  see  that  if  a  species  were 
subjected  to  unfavourable  conditions  from  severe  com- 
petition with  other  plants,  or  from  any  other  cause,  the 
production  of  the  male  and  female  elements  and  the 
maturation  of  the  ovules  by  the  same  individual  might 
prove  too  great  a  strain  on  its  powers,  and  the  separa- 
tion of  the  sexes  would  then  be  highly  beneficial. 


280  DKECIOUS  AND  CHAP.  VII. 

This,  however,  would  be  effected  only  under  the  con- 
tingency of  a  reduced  number  of  seeds,  produced  by 
the  females  alone,  being  sufficient  to  keep  up  the 
stock. 

There  is  another  way  of  looking  at  the  subject  which 
partially  removes  a  difficulty  that  appears  at  first  sight 
insuperable,  namely,  that  during  the  conversion  of  an 
hermaphrodite  into  a  dioecious  plant,  the  male  organs 
must  abort  in  some  individuals  and  the  female  organs 
in  others.  Yet  as  all  are  exposed  to  the  same  con- 
ditions, it  might  have  been  expected  that  those  which 
varied  would  tend  to  vary  in  the  same  manner.  As 
a  general  rule,  only  a  few  individuals  of  a  species 
vary  simultaneously  in  the  same  manner;  and  there 
is  no  improbability  in  the  assumption  that  some 
few  individuals  might  produce  larger  seeds  than  the 
average,  better  stocked  with  nourishment.  If  the  pro- 
duction of  such  seeds  were  highly  beneficial  to  a  species, 
and  on  this  head  there  can  be  little  doubt,*  the 
variety  with  the  large  seeds  would  tend  to  increase. 
But  in  accordance  with  the  law  of  compensation  we 
might  expect  that  the  individuals  which  produced  such 
seeds  would,  if  living  under  severe  conditions,  tend 
to  produce  less  and  less  pollen,  so  that  their  anthers 
would  be  reduced  in  size  and  might  ultimately  become 
rudimentary.  This  view  occurred  to  me  owing  to 
a  statement  by  Sir  J.  E.  Smith  f  that  there  are  female 
and  hermaphrodite  plants  of  Serratula  tinctoria,  and 
that  the  seeds  of  the  former  are  larger  than  those  of  the 
hermaphrodite  form.  It  may  also  be  worth  while  to 
recall  the  case  of  the  mid-styled  form  of  Lythrum  sali- 
caria,  which  produces  a  larger  number  of  seeds  than  the 


*See  the  facts  given  in   'The        t' Trans.  Linn.  Soc.,' vol.  xiii. 
Effects  of  Cross  and  Self-fertilisa-    p.  600. 
tion,'  p.  353. 


CHAP.  VII.  POLYGAMOUS  PLANTS.  281 

other  forms,  and  has  somewhat  smaller  pollen-grains 
which  have  less  fertilising  power  than  those  of  the  cor- 
responding stamens  in  the  other  two  forms ;  but  whether 
the  larger  number  of  seeds  is  the  indirect  cause  of  the 
diminished  power  of  the  pollen,  or  vice  versa,  I  know 
not.  As  soon  as  the  anthers  in  a  certain  number  of 
individuals  became  reduced  in  size  in  the  manner 
just  suggested  or  from  any  other  cause,  the  other  in- 
dividuals would  have  to  produce  a  larger  supply  of  pol- 
len; and  such  increased  development  would  tend  to 
reduce  the  female  organs  through  the  law  of  compen- 
sation, so  as  ultimately  to  leave  them  in  a  rudimen- 
tary condition;  and  the  species  would  then  become 
dioecious. 

Instead  of  the  first  change  occurring  in  the  female 
organs  we  may  suppose  that  the  male  ones  first  varied, 
so  that  some  individuals  produced  a  larger  supply  of 
pollen.  This  would  be  beneficial  under  certain  cir- 
cumstances, such  as  a  change  in  the  nature  of  the  in- 
sects which  visited  the  flowers,  or  in  their  becoming  more 
anemophilous,  for  such  plants  require  an  enormous  quan- 
tity of  pollen.  The  increased  action  of  the  male  organs 
would  tend  to  affect  through  compensation  the  female 
organs  of  the  same  flower ;  and  the  final  result  would  be 
that  the  species  would  consist  of  males  and  hermaphro- 
dites. But  it  is  of  no  use  considering  this  case  and 
other  analogous  ones,  for,  as  stated  in  the  Introduction, 
the  co-existence  of  male  and  hermaphrodite  plants  is  ex- 
cessively rare. 

It  is  no  valid  objection  to  the  foregoing  views  that 
changes  of  such  a  nature  would  be  effected  with  ex- 
treme slowness,  for  we  shall  presently  see  good  reason 
to  believe  that  various  hermaphrodite  plants  have  be- 
come or  are  becoming  dioecious  by  many  and  excessively 
small  steps.  In  the  case  of  polygamous  species  which 


282  DIOECIOUS  AND  CHAP.  VII. 

exist  as  males,  females  and  hermaphrodites,  the  latter 
would  have  to  be  supplanted  before  the  species  could  be- 
come strictly  dioecious;  but  the  extinction  of  the  her- 
maphrodite form  would  probably  not  be  difficult,  as  a 
complete  separation  of  the  sexes  appears  often  to  be  in 
some  way  beneficial.  The  males  and  females  would  also 
have  to  be  equalised  in  number,  or  produced  in  some 
fitting  proportion  for  the  effectual  fertilisation  of  the 
females. 

There  are,  no  doubt,  many  unknown  laws  which 
govern  the  suppression  of  the  male  or  female  organs 
in  hermaphrodite  plants,  quite  independently  of  any 
tendency  in  them  to  become  monoecious,  dioecious,  or 
polygamous.  We  see  this  in  those  hermaphrodites 
which  from  the  rudiments  still  present  manifestly 
once  possessed  more  stamens  or  pistils  than  they 
now  do, — even  twice  as  many,  as  a  whole  verticil  has 
often  been  suppressed.  Eobert  Brown  remarks  *  that 
"  the  order  of  reduction  or  abortion  of  the  stamina  in 
any  natural  family  may  with  some  confidence  be  pre- 
dicted," by  observing  in  other  members  of  the  family, 
in  which  their  number  is  complete,  the  order  of  the 
dehiscence  of  the  anthers;  for  the  lesser  permanence  of 
an  organ  is  generally  connected  with  its  lesser  perfec- 
tion, and  he  judges  of  perfection  by  priority  of  develop- 
ment. He  also  states  that  whenever  there  is  a  separation 
of  the  sexes  in  an  hermaphrodite  plant,  which  bears 
flowers  on  a  simple  spike,  it  is  the  females  which 
expand  first;  and  this  he  likewise  attributes  to  the 
female  sex  being  the  more  perfect  of  the  two,  but 
why  the  female  should  be  thus  valued  he  does  not  ex- 
plain. 

Plants  under  cultivation  or  changed  conditions  of 


*  'Trans.  Linn.  Soc.,'  vol.  xii.  p.  98.     Or  'Miscellaneous  Works,' 
vol.  ii.  pp.  278-81. 


CHAP.  VII.  POLYGAMOUS  PLANTS.  283 

life  frequently  become  sterile;  and  the  male  organs  are 
much  oftener  affected  than  the  female,  though  the  latter 
alone  are  sometimes  affected.  The  sterility  of  the  sta- 
mens is  generally  accompanied  by  a  reduction  in  their 
size;  and  we  may  feel  sure,  from  a  wide-spread  analogy, 
that  both  the  male  and  female  organs  would  become 
rudimentary  in  the  course  of  many  generations  if  they 
failed  altogether  to  perform  their  proper  functions.  Ac- 
cording to  Gartner,*  if  the  anthers  on  a  plant  are  con- 
tabescent  (and  when  this  occurs  it  is  always  at  a  very 
early  period  of  growth)  the  female  organs  are  some- 
times precociously  developed.  I  mention  this  case  as 
it  appears  to  be  one  of  compensation.  So  again  is  the 
well-known  fact,  that  plants  which  increase  largely  by 
stolons  or  other  such  means  are  often  utterly  barren, 
with  a  large  proportion  of  their  pollen-grains  in  a  worth- 
less condition. 

Hildebrand  has  shown  that  with  hermaphrodite 
plants  which  are  strongly  proterandrous,  the  stamens 
in  the  flowers  which  open  first  sometimes  abort;  and 
this  seems  to  follow  from  their  being  useless,  as  no 
pistils  are  then  ready  to  be  fertilised.  Conversely 
the  pistils  in  the  flowers  which  open  last  sometimes 
abort;  as  when  they  are  ready  for  fertilisation  all  the 
pollen  has  been  shed.  He  further  shows  by  means  of 
a  series  of  gradations  amongst  the  Composite,  f  that 
a  tendency  from  the  causes  just  specified  to  produce 
either  male  or  female  florets,  sometimes  spreads  to  all 
the  florets  on  the  same  head,  and  sometimes  even  to  the 
whole  plant ;  and  in  this  latter  case  the  species  becomes 
dioecious.  In  those  rare  instances  mentioned  in  the 


*  'Beitrage  znir  Kenntniss,'  &c.,  chap,    xviii.— 2nd    edit.    vol.    ii. 

p.  117  et  seq.     The  whole  subject  pp.  146-56. 

of  the  sterility  of  plants  from  va-  t  '  Ueber    die     Geschlechtsver- 

rious  causes  has  been  discussed  in  haltnisse    bei    den    Compositen,' 
my   'Variation    of   Animals  and 
Plants      under      Domestication,' 


284:  DIOECIOUS  AND  CHAP.  VII. 

Introduction,  in  which  some  of  the  individuals  of  both 
monoecious  and  hermaphrodite  plants  are  proterand- 
rous,  others  being  proterogynous,  their  conversion  into 
a  dioecious  condition  would  probably  be  much  facili- 
tated, as  they  already  consist  of  two  bodies  of  individ- 
uals, differing  to  a  certain  extent  in  their  reproductive 
functions. 

Dimorphic  heterostyled  plants  offer  still  more 
strongly  marked  facilities  for  becoming  dioecious;  for 
they  likewise  consist  of  two  bodies  of  individuals  in 
approximately  equal  numbers,  and,  what  probably  is 
more  important,  both  the  male  and  female  organs 
differ  in  the  two  forms,  not  only  in  structure  but  in 
function,  in  nearly  the  same  manner  as  do  the  repro- 
ductive organs  of  two  distinct  species  belonging  to 
the  same  genus.  Now,  if  two  species  are  subjected  to 
changed  conditions,  though  of  the  same  nature,  it  is 
notorious  that  they  are  often  affected  very  differently; 
therefore  the  male  organs,  for  instance,  in  one  form  of 
a  heterostyled  plant  might  be  affected  by  those  un- 
known causes  which  induce  abortion,  differently  from 
the  homologous  but  functionally  different  organs  in 
the  other  form;  and  so  conversely  with  the  female  or- 
gans. Thus  the  great  difficulty  before  alluded  to  is  much 
lessened  in  understanding  how  any  cause  whatever  could 
lead  to  the  simultaneous  reduction  and  ultimate  sup- 
pression of  the  male  organs  in  half  the  individuals  of 
a  species,  and  of  the  female  organs  in  the  other  half, 
whilst  all  were  subjected  to  exactly  the  same  conditions 
of  life. 

That  such  reduction  or  suppression  has  occurred 
in  some  heterostyled  plants  is  almost  certain.  The 
Rubiacea?  contained  more  heterostyled  genera  than  any 
other  family,  and  from  their  wide  distribution  we  may 
infer  that  many  of  them  became  heterostyled  at  a  re- 


CHAP.  VII.  POLYGAMOUS  PLANTS.  285 

mote  period,  so  that  there  will  have  been  ample  time 
for  some  of  the  species  to  have  been  since  rendered  dioe- 
cious. Asa  Gray  informs  me  that  Coprosma  is  dioecious, 
and  that  it  is  closely  allied  through  Nertera  to  Mitch- 
ella, which  as  we  know  is  a  heterostyled  dimorphic 
species.  In  the  male  flowers  of  Coprosma  the  stamens 
are  exserted,  and  in  the  female  flowers  the  stigmas; 
so  that,  judging  from  the  affinities  of  the  above  three 
genera,  it  seems  probable  that  an  ancient  short-styled 
form  bearing  long  stamens  with  large  anthers  and 
large  pollen-grains  (as  in  the  case  of  several  Kubia- 
ceous  genera)  has  been  converted  into  the  male  Co- 
prosma ;  and  that  an  ancient  long-styled  form  with  short 
stamens,  small  anthers  and  small  pollen-grains  has 
been  converted  into  the  female  form.  But  according 
to  Mr.  Meehan,*  Mitchella  itself  is  dioecious  in  some 
districts;  for  he  says  that  one  form  has  small  sessile 
anthers  without  a  trace  of  pollen,  the  pistil  being  per- 
fect ;  while  in  another  form  the  stamens  are  perfect  and 
the  pistil  rudimentary.  He  adds  that  plants  may  be 
observed  in  the  autumn  bearing  an  abundant  crop  of 
berries,  and  others  without  a  single  one.  Should  these 
statements  be  confirmed,  Mitchella  will  be  proved 
to  be  heterostyled  in  one  district  and  dioecious  in 
another. 

Asperula  is  likewise  a  Eubiaceous  genus,  and  from 
the  published  description  of  the  two  forms  of  A.  sco- 
paria,  an  inhabitant  of  Tasmania,  I  did  not  doubt  that 
it  was  heterostyled;  but  on  examining  some  flowers 
sent  me  by  Dr.  Hooker  they  proved  to  be  dioecious. 
The  male  flowers  have  large  anthers  and  a  very  small 
ovarium,  surmounted  by  a  mere  vestige  of  a  stigma 
without  any  style;  whilst  the  female  flowers  possess 
a  large  ovarium,  the  anthers  being  rudimentary  and 

*  'Proc.  Acad.  of  Sciences  of  Philadelphia,'  July  28,  1868,  p.  183. 


286  DKECIOUS  AND  CHAP.  VII. 

apparently  quite  destitute  of  pollen.  Considering  how 
many  Eubiaceous  genera  are  heterostyled,  it  is  a 
reasonable  suspicion  that  this  Asperula  is  descended 
from  a  heterostyled  progenitor;  but  we  should  be 
cautious  on  this  head,  for  there  is  no  improbability  in 
a  homostyled  Eubiaceous  plant  becoming  dioecious. 
Moreover,  in  an  allied  plant,  Galium  cruciatum,  the  fe- 
male organs  have  been  suppressed  in  most  of  the  lower 
flowers,  whilst  the  upper  ones  remain  hermaphrodite; 
and  here  we  have  a  modification  of  the  sexual  organs 
without  any  connection  with  heterostylism. 

Mr.  Thwaites  informs  me  that  in  Ceylon  various 
Eubiaceous  plants  are  heterostyled;  but  in  the  case  of 
Discospermum  one  of  the  two  forms  is  always  barren, 
the  ovar}r  containing  about  two  aborted  ovules  in  each 
loculus;  whilst  in  the  other  form  each  loculus  contains 
several  perfect  ovules;  so  that  the  species  appears  to 
be  strictly  dioecious. 

Most  of  the  species  of  the  South  American  genus 
^Egiphila,  a  member  of  the  Yerbenaceae,  apparently  are 
heterostyled;  and  both  Fritz  Miiller  and  myself  thought 
that  this  was  this  the  case  with  JE.  obdurata,  so  closely 
did  its  flowers  resemble  those  of  the  heterostyled  species. 
But  on  examining  the  flowers,  the  anthers  of  the  long- 
styled  form  were  found  to  be  entirely  destitute  of  pol- 
len and  less  than  half  the  size  of  those  in  the  other  form, 
the  pistil  being  perfectly  developed.  On  the  other  hand, 
in  the  short-styled  form  the  stigmas  are  reduced  to  half 
their  proper  length,  having  also  an  abnormal  appear- 
ance ;  whilst  the  stamens  are  perfect.  This  plant  there- 
fore is  dioecious;  and  we  may,  I  think,  conclude  that 
a  short-styled  progenitor,  bearing  long  stamens  exserted 
beyond  the  corolla,  has  been  converted  into  the  male; 
and  a  long-styled  progenitor  with  fully  developed  stig- 
mas into  the  female. 


CHAP.  VII.  POLYGAMOUS  PLANTS.  287 

From  the  number  of  bad  pollen-grains  in  the  small 
anthers  of  the  short  stamens  of  the  long-styled  form  of 
Pulmonaria  angustifolia,  we  may  suspect  that  this  form 
is  tending  to  become  female ;  but  it  does  not  appear  that 
the  other  or  short-styled  form  is  becoming  more  mascu- 
line. Certain  appearances  countenance  the  belief  that 
the  reproductive  system  of  Phlox  subulala  is  likewise 
undergoing  a  change  of  some  kind. 

I  have  now  given  the*  few  cases  known  to  me  in 
which  heterostyled  plants  appear  with  some  consider- 
able degree  of  probability  to  have  been  rendered  dioe- 
cious. Nor  ought  we  to  expect  to  find  many  such  cases, 
for  the  number  of  heterostyled  species  is  by  no  means 
large,  at  least  in  Europe,  where  they  could  hardly  have 
escaped  notice.  Therefore  the  number  of  dioecious  spe- 
cies which  owe  their  origin  to  the  transformation  of 
heterostyled  plants  is  probably  not  so  large  as  might  have 
been  anticipated  from  the  facilities  which  they  offer  for 
such  conversion. 

In  searching  for  cases  like  the  foregoing  ones,  I  have 
been  led  to  examine  some  dioecious  or  sub-dioecious 
plants,  which  are  worth  describing,  chiefly  as  they  show 
by  what  fine  gradations  hermaphrodites  may  pass  into 
polygamous  or  difficious  species. 

Polygamous,  Dioecious  and  Sub-dioecious  Plants* 
Euonymus  Europceus  (Celastrinese). — The  spindle- 
tree  is  described  in  all  the  botanical  works  which  I  have 
consulted  as  an  hermaphrodite.  Asa  Gray  speaks  of 
the  flowers  of  the  American  species  as  perfect,  whilst 
those  in  the  allied  genus  Celastrus  are  said  to  be 
"  polygamo-dioecious."  If  a  number  of  bushes  of  our 
spindle-tree  be  examined,  about  half  will  be  found  to 
have  stamens  equal  in  length  to  the  pistil,  with  well- 
developed  anthers;  the  pistil  being  likewise  to  all  ap- 


288 


DIOECIOUS  AND 


CHAP.  VII. 


pearance  well-developed.  The  other  half  have  a  perfect 
pistil,  with  the  stamens  short,  bearing  rudimentary  an- 
thers destitute  of  pollen;  so  that  these  bushes  are  fe- 
males. All  the  flowers  on  the  same  plant  present  the 
same  structure.  The  female  corolla  is  smaller  than  that 
on  the  polleniferous  bushes.  The  two  forms  are  shown 
in  the  accompanying  drawings. 


Hermaphrodite  or  male.  Female. 

EUONYMUS  EUROP.EUS. 

I  did  not  at  first  doubt  that  this  species  existed  under 
an  hermaphrodite  and  female  form;  but  we  shall  pres- 
ently see  that  some  of  the  bushes  which  appear  to  be 
hermaphrodites  never  produce  fruit,  and  these  are  in 
fact  males.  The  species,  therefore,  is  polygamous  in  the 
sense  in  which  I  use  the  term,  and  trioicous.  The  flow- 
ers are  frequented  by  many  Diptera  and  some  small 
Hymenoptera  for  the  sake  of  the  nectar  secreted  by  the 
disc,  but  I  did  not  see  a  single  bee  at  work;  neverthe- 
less the  other  insects  sufficed  to  fertilise  effectually  fe- 
male bushes  growing  at  a  distance  of  even  30  yards  from 
any  polleniferous  bush. 

The  small  anthers  borne  by  the  short  stamens  of 
the  female  flowers  are  well  formed  and  dehisce  prop- 
erly, but  I  could  never  find  in  them  a  single  grain 
of  pollen.  It  is  somewhat  difficult  to  compare  the 


CHAP.  VII.  POLYGAMOUS  PLANTS.  289 

length  of  the  pistils  in  the  two  forms,  as  they  vary 
somewhat  in  this  respect  and  continue  to  grow  after 
the  anthers  are  mature.  The  pistils,  therefore,  in  old 
flowers  on  a  polleniferous  plant  are  often  of  consider- 
ably greater  length  than  in  young  flowers  on  a  female 
plant.  On  this  account  the  pistils  from  five  flowers 
from  so  many  hermaphrodite  or  male  bushes  were 
compared  with  those  from  five  female  bushes,  before 
the  anthers  had  dehisced  and  whilst  the  rudimentary 
ones  were  of  a  pink  colour  and  not  at  all  shrivelled. 
These  two  sets  of  pistils  did  not  differ  in  length,  or  if 
there  was  any  difference  those  of  the  polleniferous 
flowers  were  rather  the  longest.  In  one  hermaphrodite 
plant,  which  produced  during  three  years  very  few 
and  poor  fruit,  the  pistil  much  exceeded  in  length 
the  stamens  bearing  perfect  and  as  yet  closed  an- 
thers; and  I  never  saw  such  a  case  on  any  female 
plant.  It  is  a  surprising  fact  that  the  pistil  in  the 
male  and  in  the  semi-sterile  hermaphrodite  flowers 
has  not  been  reduced  in  length,  seeing  that  it  per- 
forms very  poorly  or  not  at  all  its  proper  function. 
The  stigmas  in  the  two  forms  are  exactly  alike;  and 
in  some  of  the  polleniferous  plants  which  never  pro- 
duced any  fruit  I  found  that  the  surface  of  the  stigma 
was  viscid,  so  that  pollen-grains  adhered  to  it  and  had 
exserted  their  tubes.  The  ovules  are  of  equal  size  in  the 
two  forms.  Therefore  the  most  acute  botanist,  judging 
only  by  structure,  ,would  never  have  suspected  that  some 
of  the  bushes  were  in  function  exclusively  males. 

Thirteen  bushes  growing  near  one  another  in  a 
hedge  consisted  of  eight  females  quite  destitute  of 
pollen  and  of  five  hermaphrodites  with  well-developed 
anthers.  In  the  autumn  the  eight  females  were  well 
covered  with  fruit,  excepting  one,  which  bore  only  a 
moderate  number.  Of  the  five  hermaphrodites,  one 


290  DKECIOUS  AND  CHAP.  VII. 

bore  a  dozen  or  two  fruits,  and  the  remaining  four 
bushes  several  dozen;  but  their  number  was  as  nothing 
compared  with  those  on  the  female  bushes,  for  a  single 
branch,  between  two  and  three  feet  in  length,  from 
one  of  the  latter,  yielded  more  than  any  one  of  the 
hermaphrodite  bushes.  The  difference  in  the  amount 
of  fruit  produced  by  the  two  sets  of  bushes  is  all  the 
more  striking,  as  from  the  sketches  above  given  it  is 
obvious  that  the  stigmas  of  the  polleniferous  flowers  can 
hardly  fail  to  receive  their  own  pollen;  whilst  the  fer- 
tilisation of  the  female  flowers  depends  on  pollen  being 
brought  to  them  by  flies  and  the  smaller  Hymenoptera, 
which  are  far  from  being  such  efficient  carriers  as  bees. 

I  now  determined  to  observe  more  carefully  during 
successive  seasons  some  bushes  growing  in  another 
place  about  a  mile  distant.  As  the  female  bushes 
were  so  highly  productive,  I  marked  only  two  of  them 
with  the  letters  A  and  B,  and  five  polleniferous  bushes 
with  the  letters  C  to  G.  I  may  premise  that  the 
year  1865  was  highly  favourable  for  the  fruiting  of  all 
the  bushes,  especially  for  the  polleniferous  ones,  some 
of  which  were  quite  barren  except  under  such  favour- 
able conditions.  The  season  of  1864  was  unfavourable. 
In  1863  the  female  A  produced  "  some  fruit; "  in  1864 
only  9;  and  in  1865,  97  fruit.  The  female  B  in  1863 
was  "covered  with  fruit;"  in  1864  it  bore  28;  and  in 
1865  "innumerable  very  fine  fruits."  I  may  add 
that  three  other  female  trees  growing  close  by  were 
observed,  but  only  during  1863,  and  they  then  bore 
abundantly.  With  respect  to  the  polleniferous  bushes, 
the  one  marked  C  did  not  bear  a  single  fruit  during 
the  years  1863  and  1864,  but  during  1865  it  produced 
no  less  than  92  fruit,  which,  however,  were  very  poor. 
I  selected  one  of  the  finest  branches  with  15  fruit,  and 
these  contained  20  seeds,  or  on  an  average  1.33  per 


CHAP.  VII.  POLYGAMOUS  PLANTS.  291 

fruit.  I  then  took  by  hazard  15  fruit  from  an  adjoin- 
ing female  bush,  and  these  contained  43  seeds;  that 
is  more  than  twice  as  many,  or  on  an  average  2.86 
per  fruit.  Many  of  the  fruits  from  the  female  bushes 
included  four  seeds,  and  only  one  had  a  single  seed; 
whereas  not  one  fruit  from  the  polleniferous  bushes 
contained  four  seeds.  Moreover,  when  the  two  lots  of 
seeds  were  compared,  it  was  manifest  that  those  from 
the  female  bushes  were  the  larger.  The  second  pollen- 
iferous bush,  D,  bore  in  1863  about  two  dozen  fruit, — 
in  1864  only  3  very  poor  fruit,  each  containing  a  single 
seed, — and  in  1865,  20  equally  poor  fruit.  Lastly,  the 
three  polleniferous  bushes,  E,  F,  and  G,  did  not  pro- 
duce a  single  fruit  during  the  three  years  1863,  1864, 
and  1865. 

We  thus  see  that  the  female  bushes  differ  somewhat 
in  their  degree  of  fertility,  and  the  polleniferous  ones 
in  the  most  marked  manner.  We  have  a  perfect  grada- 
tion from  the  female  bush,  B,  which  in  1865  was  covered 
with  "  innumerable  rniit," — through  the  female  A, 
which  produced  during  the  same  year  97, — through  the 
polleniferous  bush  C,  which  produced  this  year  92  fruits, 
these,  however,  containing  a  very  low  average  number  of 
seeds  of  small  size, — through  the  bush  D,  which  pro- 
duced only  20  poor  fruit, — to  the  three  bushes,  E,  F, 
and  G,  which  did  not  this  year,  or  during  the  two  pre- 
vious years,  produce  a  single  fruit.  If  these  latter 
bushes  and  the  more  fertile  female  ones  were  to  supplant 
the  others,  the  spindle-tree  would  be  as  strictly  dioecious 
in  function  as  any  plant  in  the  world.  This  case  appears 
to  me  very  interesting,  as  showing  how  gradually  an  her- 
maphrodite plant  may  be  converted  into  a  dioecious  one.* 


*  According  to  Fritz  Miiller  Southern  Brazil  is  in  nearly  the 
("Bot.  Zeitung.'  1870.  p.  151),  a  same  state  as  our  Euonymus.  The 
Chamissoa  (Amaranthacese)  in  ovules  are  equally  developed  in 


292  DICECIOUS  AND  CHAP.  VII. 

Seeing  how  general  it  is  for  organs  which  are 
almost  quite  functionless  to  be  reduced  in  size,  it  is 
remarkable  that  the  pistils  of  the  polleniferous  plants 
should  equal  or  even  exceed  in  length  those  of  the 
highly  fertile  female  plants.  This  fact  formerly  led 
me  to  suppose  that  the  spindle-tree  had  once  been 
heterostyled ;  the  hermaphrodite  and  male  plants  hav- 
ing been  originally  long-styled,  with  the  pistils  since 
reduced  in  length,  but  with  the  stamens  retaining 
their  former  dimensions;  whilst  the  female  plant  had 
been  originally  short-styled,  with  the  pistil  in  its  pres- 
ent state,  but  with  the  stamens  since  greatly  reduced 
and  rendered  rudimentary.  A  conversion  of  this  kind 
is  at  least  possible,  although  it  is  the  reverse  of 
that  which  appears  actually  to  have  occurred  with 
some  Eubiaceous  genera  and  ^Egiphila;  for  with  these 
plants  the  short-styled  form  has  become  the  male,  and 
the  long-styled  the  female.  It  is,  however,  a  more 
simple  view  that  sufficient  time  has  not  elapsed  for  the 
reduction  of  the  pistil  in  the  male  and  hermaphrodite 
flowers  of  our  Euonymus;  though  this  view  does  not 
account  for  the  pistils  in  the  polleniferous  flowers 
being  sometimes  longer  than  those  in  the  female 
flowers. 

Fragaria  vesca,  Virginiana,  Chiloensis,  &c.  (Eosa- 
ceee). — A  tendency  to  the  separation  of  the  sexes  in  the 
cultivated  strawberry  seems  to  be  much  more  strongly 
marked  in  the  United  States  than  in  Europe;  and 
this  appears  to  be  the  result  of  the  direct  action  of 


the  two  forms.    In  the  female,  the  These  latter  plants  do  not  com- 

pistil  is  perfect,  whilst  the  anthers  monly  yield  any  fruit,   and  are 

are  entirely  destitute   of  pollen,  therefore  in  function  males.   Nev- 

In  the  polleniferous  form,  the  pis-  ertheless,  on    one  occasion  Fritz 

til  is  short  and  the  stigmas  never  Miiller  found  flowers  of  this  kind 

separate  from  one  another,  so  that,  in  which   the  stigmas  had  sepa- 

although  their  surfaces   are  cov-  rated,   and  they  produced    some 

ered  with  fairly  well-developed  pa-  fruit, 
pillae,  they  cannot  be  fertilised. 


CHAP.  VII.  POLYGAMOUS  PLANTS.  293 

climate  on  the  reproductive  organs.  In  the  best  ac- 
count which  I  have  seen,*  it  is  stated  that  many  of  the 
varieties  in  the  United  States  consist  of  three  forms, 
namely,  females,  which  produce  a  heavy  crop  of  fruit, — 
of  hermaphrodites,  which  "  seldom  produce  other  than 
a  very  scanty  crop  of  inferior  and  imperfect  berries," 
— and  of  males,  which  produce  none.  The  most  skilful 
cultivators  plant  "  seven  rows  of  female  plants,  then 
one  row  of  hermaphrodites,  and  so  on  throughout  the 
field."  The  males  bear  large,  the  hermaphrodites 
mid-sized,  and  the  females  small  flowers.  The  latter 
plants  produce  few  runners,  whilst  the  two  other  forms 
produce  many;  consequently,  as  has  been  observed 
both  in  England  and  in  the  United  States,  the  polleni- 
ferous  forms  increase  rapidly  and  tend  to  supplant  the 
females.  We  may  therefore  infer  that  much  more  vital 
force  is  expended  in  the  production  of  ovules  and  fruit 
than  in  the  production  of  pollen.  Another  species,  the 
Hautbois  strawberry  (F.  elatior),  is  more  strictly  dioe- 
cious; but  Lindley  made  by  selection  an  hermaphrodite 
stock,  f 

Rhamnus  catharticus  (Rhamnene). — This  plant  is 
well  known  to  be  dioecious.  My  son  William  found  the 
two  sexes  growing  in  about  equal  numbers  in  the  Isle 
of  Wight,  and  sent  me  specimens,  together  with  obser- 
vations on  them.  Each  sex  consists  of  two  sub-forms. 
The  two  forms  of  the  male  differ  in  their  pistils:  in 
some  plants  it  is  quite  small,  without  any  distinct  stig- 
ma; in  others  the  pistil  is  much  more  developed,  with 
the  papillae  on  the  stigmatic  surfaces  moderately  large. 
The  ovules  in  both  kinds  of  males  are  in  an  aborted  con- 
dition. On  my  mentioning  this  case  to  Professor  Cas- 


*  Mr.  Leonard  Wray  in  '  Gard.    formation    on    this    subject,     see 
Chron,'  1861,  p.  716.  'Variation  under  Domestication,' 

t  For  references  and  further  in-    chap.  x.  2nd  edit.  vol.  i.  p.  375. 


294:  DICECIOUS  AND  CHAP.  VII. 

pary,  he  examined  several  male  plants  in  the  botanic 
gardens  at  Konigsberg,  where  there  were  no  females,  and 
sent  me  the  accompanying  drawings. 


Fig.  13. 


Long-styled  male.  Short-styled  male. 

EHAMNUS  CATHABTTCUS.    (From  Caspary.) 

In  the  English  plants  the  petals  are  not  so  greatly 
reduced  as  represented  in  this  drawing.  My  son  ob- 
served that  those  males  which  had  their  pistils  moder- 
ately well  developed  bore  slightly  larger  flowers,  and, 
what  is  very  remarkable,  their  pollen-grains  exceeded 
by  a  little  in  diameter  those  of  the  males  with  greatly 
reduced  pistils.  This  fact  is  opposed  to  the  belief  that 
the  present  species  was  once  heterostyled ;  for  in  this 
case  it  might  have  been  expected  that  the  shorter-styled 
plants  would  have  had  larger  pollen-grains. 

In  the  female  plants  the  stamens  are  in  an  ex- 
tremely rudimentary  condition,  much  more  so  than 
the  pistils  in  the  males.  The  pistil  varies  consid- 
erably in  length  in  the  female  plants,  so  that  they 
may  be  divided  into  two  sub-forms  according  to  the 
length  of  this  organ.  Both  the  petals  and  sepals  are 
decidedly  smaller  in  the  females  than  in  the  males; 
and  the  sepals  do  not  turn  downwards,  as  do  those  of 
the  male  flowers  when  mature.  All  the  flowers  on  the 
same  male  or  same  female  bush,  though  subject  to 
some  variability,  belong  to  the  same  sub-form;  and 
as  my  son  never  experienced  any  difficulty  in  decid- 


CHAP.  VII.  POLYGAMOUS  PLANTS.  295 

ing  under  which  class  a  plant  ought  to  be  included, 
he  believes  that  the  two  sub-forms  of  the  same  sex 
do  not  graduate  into  one  another.  I  can  form  no 
satisfactory  theory  how  the  four  forms  of  this  plant 
originated. 

Rhamnus  lanceolatus  exists  in  the  United  States, 
as  I  am  informed  by  Professor  Asa  Gray,  under  two 
hermaphrodite  forms.  In  the  one,  which  may  be  called 
the  short-styled,  the  flowers  are  sub-solitary,  and  in- 
clude a  pistil  about  two-thirds  or  only  half  as  long  as 
that  in  the  other  form ;  it  has  also  shorter  stigmas.  The 
stamens  are  of  equal  length  in  the  two  forms;  but  the 
anthers  of  the  short-styled  contain  rather  less  pollen, 
as  far  as  I  could  judge  from  a  few  dried  flowers.  My 

Fig.  14. 


Long-styled 
female. 

RHAMNUS  CATHAKTICUS. 

son  compared  the  pollen-grains  from  the  two  form.?, 
and  those  from  the  long-styled  flowers  were  to  those 
from  the  short-styled,  on  an  average  from  ten  measure- 
ments, as  10  to  9  in  diameter;  so  that  the  two  her- 
maphrodite forms  of  this  species  resemble  in  this 
respect  the  two  male  forms  of  R.  catharticus.  The  long- 
styled  form  is  not  so  common  as  the  short-styled.  The 
latter  is  said  by  Asa  Gray  to  be  the  more  fruitful 
of  the  two,  as  might  have  been  expected  from  its  ap- 
pearing to  produce  less  pollen,  and  from  the  grains 


296  DIOECIOUS  AND  CHAP.  VII. 

being  of  smaller  size;  it  is  therefore  the  more  highly 
feminine  of  the  two.  The  long-styled  form  produces 
a  greater  number  of  flowers,  which  are  clustered  to- 
gether instead  of  being  sub-solitary;  they  yield  some 
fruit,  but  as  just  stated  are  less  fruitful  than  the  other 
form,  so  that  this  form  appears  to  be  the  more  mas- 
culine of  the  two.  On  the  supposition  that  we  have 
here  an  hermaphrodite  plant  becoming  dioecious,  there 
are  two  points  deserving  notice;  firstly,  the  greater 
length  of  the  pistil  in  the  incipient  male  form;  and  we 
have  met  with  a  nearly  similar  case  in  the  male  and 
hermaphrodite  forms  of  Euonymus  compared  with  the 
females.  Secondly,  the  larger  size  of  the  pollen-grains 
in  the  more  masculine  flowers,  which  perhaps  may  be 
attributed  to  their  having  retained  their  normal  size; 
whilst  those  of  the  incipient  female  flowers  have  been 
reduced.  The  long-styled  form  of  R.  lanceolatus  seems 
to  correspond  with  the  males  of  E.  catharlicus  which 
have  a  longer  pistil  and  larger  pollen-grains.  Light  will 
perhaps  be  thrown  on  the  nature  of  the  forms  in  this 
genus,  as  soon  as  the  power  of  both  kinds  of  pollen  on 
both  stigmas  is  ascertained.  Several  other  species  of 
Ehamnus  are  said  to  be  dioecious  *  or  sub  dioecious.  On 
the  other  hand,  R.  frangula  is  an  ordinary  hermaphro- 
dite, for  my  son  found  a  large  number  of  bushes  all  bear- 
ing an  equal  profusion  of  fruit. 

Epigcea  repens  (Ericaceae). — This  plant  appears  to 
be  in  nearly  the  same  state  as  Rhamnus  catharticus. 
It  is  described  by  Asa  Gray  f  as  existing  under  four 
forms.  (1)  With  long  style,  perfect  stigma,  and  short 
abortive  stamens.  (2)  Shorter  style,  but  with  stigma 
equally  perfect,  short  abortive  stamens.  These  two 


*Lecoq,  'Ge"ogr.  Bot.'  torn.  v.    July,  1876.    Also,  'The  American 
1856,  pp.  420-26.  Naturalist,'  1876,  p.  490. 

t  '  American  Journal  of  Science,' 


CHAP.  VIL  POLYGAMOUS  PLANTS.  397 

female  forms  amounted  to  20  per  cent,  of  the  speci- 
mens received  from  one  locality  in  Maine;  but  all 
the  fruiting  specimens  belonged  to  the  first  form. 
(3)  Style  long,  as  in  No.  1,  but  with  stigma  imperfect, 
stamens  perfect.  (4)  Style  shorter  than  in  the  last, 
stigma  imperfect,  stamens  perfect.  These  two  latter 
forms  are  evidently  males.  Therefore,  as  Asa  Gray 
remarks,  "  the  flowers  may  be  classified  into  two 
kinds,  each  with  two  modifications;  the  two  main  kinds 
characterised  by  the  nature  and  perfection  of  the  stig- 
ma, along  with  more  or  less  abortion  of  the  stamens; 
their  modifications,  by  the  length  of  the  style."  Mr. 
Meehan  has  described  *  the  extreme  variability  of 
the  corolla  and  calyx  in  this  plant,  and  shows  that  it 
is  dioscious.  It  is  much  to  be  wished  that  the  pollen- 
grains  in  the  two  male  forms  should  be  compared, 
and  their  fertilising  power  tried  on  the  two  female 
forms. 

Ilex  aquifolium  (Aquifoliaceae). — In  the  several 
works  which  I  have  consulted,  one  author  alone  f  says 
that  the  holly  is  direcious.  During  several  years  I  have 
examined  many  plants,  but  have  never  found  one  that 
was  really  hermaphrodite.  I  mention  this  genus  because 
the  stamens  in  the  female  flowers,  although  quite  des- 
titute of  pollen,  are  but  slightly  arjd  sometimes  not  at 
all  shorter  than  the  perfect  stamens  in  the  male  flowers. 
In  the  latter  the  ovary  is  small  and  the  pistil  is  almost 
aborted.  The  filaments  of  the  perfect  stamens  adhere 
for  a  greater  length  to  the  petals  than  in  the  female 
flowers.  The  corolla  of  the  latter  is  rather  smaller 
than  that  of  the  male.  The  male  trees  produce  a 
greater  number  of  flowers  than  the  females.  Asa  Gray 


*  "Variations  in  Epicjxa  re  wns,"  t  Vanch*r,     'Hist.     Phys.     des 

'  Proc.  Acid.   Nat.  Soc.   of  Phila-  Plantes  d'Europe,'   1841,   torn.  ii. 

delphia,'  May  1868,  p.  153.  p.  11. 
21 


298  DICECIOUS  AND  CHAP.  VII. 

informs  me  that  I.  opaca,  which  represents  in  the  United 
States  our  common  holly,  appears  (judging  from  dried 
flowers)  to  be  in  a  similar  state;  and  so  it  is,  accord- 
ing to  Vaucher,  with  several  other  but  not  with  all  the 
species  of  the  genus. 

Gyno-dicecious  Plants. 

The  plants  hitherto  described  either  show  a  tendency 
to  become  dioecious,  or  apparently  have  become  so 
within  a  recent  period.  But  the  species  now  to  be 
considered  consist  of  hermaphrodites  and  females 
without  males,  and  rarely  show  any  tendency  to 
be  dioecious,  as  far  as  can  be  judged  from  their 
present  condition  and  from  the  absence  of  species 
having  separated  sexes  within  the  same  groups. 
Species  belonging  to  the  present  class,  which  I  have 
called  gyno-dicecious,  are  found  in  various  widely 
distinct  families;  but  are  much  more  common  in  the 
Labiatae  (as  has  long  been  noticed  by  botanists)  than 
in  any  other  group.  Such  cases  have  been  noticed  by 
myself  in  Tliymus  serpyllum  and  vulgaris,  Satureia 
liortensis,  Origanum  vulgare,  and  Mentha  hirsuta;  and 
by  others  in  Nepeta  glechoma,  Mentha  vulgaris  and 
aquatica,  and  Prunella  vulgaris.  In  these  two  latter 
species  the  female  form,  according  to  H.  Miiller,  is  in- 
frequent. To  these  must  be  added  Dracocephalum 
Moldavicum,  Melissa  officinalis  and  clinipodium,  and 
Hyssopus  officinalis.*  In  the  two  last-named  plants  the 


*H.  Miiller,  'Die  Befrnchtung  and  Lecoq  were  mistaken  in  think- 

der  Blumen,'  1873;  and 'Nature,'  ing    that    several    of  the    plants 

1873,   p.    161.     Vaucher,    '  Plantes  named  in   the  text  are  dioecious. 

d'Europe,'   torn.   iii.  p.   611.     For  They  appear  to  have  assumed  that 

Dracocephalum,       Schimper,      as  the    hermaphrodite    form    was    a 

quoted    by  Braun,    '  Annals   and  male  ;  perhaps  they  were  deceived 

Mag.  of  Nat.  Hist.'  2nd  series,  vol.  by  the  pistil  not  becoming  fully 

xviii.  1856,  p.  380.     Lecoq,  'Geo-  developed  and   of  proper    length 

graphic  Bot.  del'Europe,' tom.viii.  until  some  time  after  the  anthers 

pp.  33,  38,  44,  &c.     Both  Vaucher  have  dehisced. 


CHAP.  VII.          GYNO-DICECIOUS  PLANTS.  299 

female  form  likewise  appears  to  be  rare,  for  I  raised 
many  seedlings  from  both,  and  all  were  hermaphrodites. 
It  has  already  been  remarked  in  the  Introduction  that 
andro-dicecious  species,  as  they  may  be  called,  or  those 
which  consist  of  hermaphrodites  and  males,  are  extreme- 
ly rare,  or  hardly  exist. 

Thymus  serpyllum. — The  hermaphrodite  plants  pre- 
sent nothing  particular  in  the  state  of  their  reproduc- 
tive organs ;  and  so  it  is  in  all  the  following  cases.  The 
females  of  the  present  species  produce  rather  fewer 
flowers  and  have  somewhat  smaller  corollas  than  the 
hermaphrodites;  so  that  near  Torquay,  where  this 
plant  abounds,  I  could,  after  a  little  practice,  distin- 
guish the  two  forms  whilst  walking  quickly  past  them. 
According  to  Vaucher,  the  smaller  size  of  the  corolla 
is  common  to  the  females  of  most  or  all  of  the  above- 
mentioned  Labiatae.  The  pistil  of  the  female,  though 
somewhat  variable  in  length,  is  generally  shorter, 
with  the  margins  of  the  stigma  broader  and  formed 
of  more  lax  tissue,  than  that  of  the  hermaphrodite. 
The  stamens  in  the  female  vary  excessively  in  length; 
they  are  generally  enclosed  within  the  tube  of  the 
corolla,  and  their  anthers  do  not  contain  any  sound 
pollen;  but  after  long  search  I  found  a  single  plant 
with  the  stamens  moderately  exserted,  and  their  an- 
thers contained  a  very  few  full-sized  grains,  together 
with  a  multitude  of  minute  empty  ones.  In  some  fe- 
males the  stamens  are  extremely  short,  and  their  minute 
anthers,  though  divided  into  the  two  normal  cells  or 
loculi,  contained  not  a  trace  of  pollen:  in  others  again 
the  anthers  did  not  exceed  in  diameter  the  filaments 
which  supported  them,  and  were  not  divided  into  two 
loculi.  Judging  from  what  I  have  myself  seen  and 
from  the  descriptions  of  others,  all  the  plants  in  Brit- 
ain, Germany,  and  near  Mentone,  are  in  the  state  just 


300  GYNO-DICECIOUS  PLANTS.  CHAP.  VII. 

described;  and  I  have  never  found  a  single  flower 
with  an  aborted  pistil.  It  is,  therefore,  remarkable 
that  according  to  Delpino,*  this  plant  near  Florence  is 
generally  trimorphic,  consisting  of  males  with  aborted 
pistils,  females  with  aborted  stamens  and  hermaphro- 
dites. 

I  found  it  very  difficult  to  judge  of  the  proportional 
number  of  the  two  forms  at  Torquay.  They  often 
grow  mingled  together,  but  with  large  patches  con- 
sisting of  one  form  alone.  At  first  I  thought  that  the 
two  were  nearly  equal  in  number;  but  on  examining 
every  plant  which  grew  close  to  the  edge  of  a  little 
overhanging  dry  cliff,  about  200  yards  in  length,  I 
found  only  12  females;  all  the  rest,  some  hundreds 
in  number,  being  hermaphrodites.  Again,  on  an 
extensive  gently  sloping  bank,  which  was  so  thickly 
covered  with  this  plant  that,  viewed  from  a  distance 
of  half  a  mile  it  appeared  of  a  pink  colour,  I  could 
not  discover  a  single  female.  Therefore  the  her- 
maphrodites must  greatly  exceed  in  number  the  fe- 
males, at  least  in  the  localities  examined  by  me.  A 
very  dry  station  apparently  favours  the  presence 
of  the  female  form.  With  some  of  the  other  above- 
named  Labiatae  the  nature  of  the  soil  or  climate 
likewise  seems  to  determine  the  presence  of  one  or 
both  forms;  thus  with  Nepeta  glechoma,  Mr.  Hart 
found  in  1873  that  all  the  plants  which  he  examined 
near  Kilkenny  in  Ireland  were  females;  whilst  all  near 
Bath  were  hermaphrodites,  and  near  Hertford  both 
forms  were  present,  but  with  a  preponderance  of  her- 
maphrodites, f  "  It  would,  however,  be  a  mistake  to 
suppose  that  the  nature  of  the  conditions  determines 


*  '  Sull'  Opera  la    Distribuzione    H.    Miillor,      '  Die    Befruchtung, 
del  Sessi  nello  Piante.  &c.,'  1867,     &c.,'  r>.  327. 
p.   7.    With  respect  to   Germany,        f  '  Nature,'  June  1873,  p.  162. 


CHAP.  VII.  GYXO-DIGECIOUS  PLANTS.  301 

the  form  independently  of  inheritance;  for  I  sowed 
in  the  same  small  bed  seeds  of  T.  serpyllum,  gathered 
at  Torquay  from  the  female  alone,  and  these  produced 
an  abundance  of  both  forms.  There  is  every  reason 
to  believe,  from  large  patches  consisting  of  the  same 
form,  that  the  same  individual  plant,  however  much 
it  may  spread,  always  retains  the  same  form.  In  two 
distant  gardens  I  found  masses  of  the  lemon-thyme  (T. 
citriodorus,  a  var.  of  T.  serpyllum},  which  I  was  in- 
formed had  grown  there  during  many  years,  and  every 
flower  was  female. 

With  respect  to  the  fertility  of  the  two  forms,  I 
marked  at  Torquay  a  large  hermaphrodite  and  a  large 
female  plant  of  nearly  equal  sizes,  and  when  the  seeds 
were  ripe  I  gathered  all  the  heads.  The  two  heaps  were 
of  very  nearly  equal  bulk;  but  the  heads  from  the  fe- 
male plant  numbered  160,  and  their  seeds  weighed  8.7 
grains;  whilst  those  from  the  hermaphrodite  plant  num- 
bered 200,  and  their  seeds  weighed  only  4.9  grains;  so 
that  the  seeds  from  the  female  plant  were  to  those  from 
the  hermaphrodite  as  100  to  56  in  weight.  If  the  rela- 
tive weight  of  the  seeds  from  an  equal  number  of 
flower-heads  from  the  two  forms  be  compared,  the  ratio 
is  as  100  for  the  female  to  45  for  the  hermaphrodite 
form. 

Thymus  vulgaris. — The  common  garden  thyme  re- 
sembles in  almost  every  respect  T.  serpyllum.  The 
same  slight  differences  between  the  stigmas  of  the  two 
forms  could  be  perceived.  In  the  females  the  stamens 
are  not  generally  quite  so  much  reduced  as  in  the  same 
form  of  T.  serpyllum.  In  some  specimens  sent  me 
from  Mentone  by  Mr.  Moggridge,  together  with  the  ac- 
companying sketches,  the  anthers  of  the  female,  though 
small,  were  well  formed,  but  they  contained  very  little 
pollen,  and  not  a  single  sound  grain  could  be  de- 


302 


GYNO-DKECIOUS  PLANTS. 


CHAP.  VII. 


tected.  Eighteen  seedlings  were  raised  from  purchased 
seed,  sown  in  the  same  small  bed;  and  these  consisted 
of  seven  hermaphrodites  and  eleven  females.  They 
were  left  freely  exposed  to  the  visits  of  bees,  and  no 

Fig.  15. 


Hermaphrodite.  Females. 

THYMCS  VULGAKIS  (magnified). 

doubt  every  female  flower  was  fertilised;  for  on  plac- 
ing under  the  microscope* a  large  number  of  stigmas 
from  female  plants,  not  one  could  be  found  to  which 
pollen-grains  of  thyme  did  not  adhere.  The  seeds 
were  carefully  collected  from  the  eleven  female  plants, 
and  they  weighed  98.7  grains;  and  those  from  the 
seven  hermaphrodites  36.5  grains.  This  gives  for  an 
equal  number  of  plants  the  ratio  of  100  to  58; 
and  we  here  see,  as  in  the  last  case,  how  much  more 
fertile  the  females  are  than  the  hermaphrodites.  These 
two  lots  of  seeds  were  sown  separately  in  two  ad- 
joining beds,  and  the  seedlings  from  both  the  her- 
maphrodite and  female  parent-plants  consisted  of  both 
forms. 

Satureia  Jiortcnsis. — Eleven  seedlings  were  raised  in 
separate  pots  in  a  hotbed  and  afterwards  kept  in  the 
green-house.  They  consisted  of  ten  females  and  of  a 
single  hermaphrodite.  Whether  or  not  the  conditions 
to  which  they  had  been  subjected  caused  the  great  ex- 


CHAP.  VII.  GYNO-DKECIOUS  PLANTS.  3Q3 

cess  of  females  I  do  not  know.  In  the  females  the 
pistil  is  rather  longer  than  that  of  the  hermaphrodite, 
and  the  stamens  are  mere  rudiments,  with  minute  col- 
ourless anthers  destitute  of  pollen.  The  windows  of  the 
green-house  were  left  open,  and  the  flowers  were  inces- 
santly visited  by  humble  and  hive  bees.  Although  the 
ten  females  did  not  produce  a  single  grain  of  pollen, 
yet  they  were  all  thoroughly  well  fertilised  by  the  one 
hermaphrodite  plant,  and  this  is  an  interesting  fact. 
It  should  be  added  that  no  other  plant  of  this  species 
grew  in  my  garden.  The  seeds  were  collected  from  the 
finest  female  plant,  and  they  weighed  78  grains;  whilst 
those  from  the  hermaphrodite,  which  was  a  rather  larger 
plant  than  the  female,  weighed  only  33.2  grains;  that 
is,  in  the  ratio  of  100  to  43.  The  female  form,  there- 
fore, is  very  much  more  fertile  than  the  hermaphrodite, 
as  in  the  two  last  cases;  but  the  hermaphrodite  Was 
necessarily  self-fertilised,  and  this  probably  diminished 
its  fertility. 

We  may  now  consider  the  probable  means  by  which 
so  many  of  the  Labiatse  have  been  separated  into  two 
forms,  and  the  advantages  thus  gained.  H.  Miiller  * 
supposes  that  originally  some  individuals  varied  so  as 
to  produce  more  conspicuous  flowers;  and  that  insects 
habitually  visited  these  first,  and  then  dusted  with 
their  pollen  visited  and  fertilised  the  less  conspicuous 
flowers.  The  production  of  pollen  by  the  latter  plants 
would  thus  be  rendered  superfluous,  and  it  would  be 
advantageous  to  the  species  that  their  stamens  should 
abort,  so  as  to  save  useless  expenditure.  They  would 
thus  be  converted  into  females.  But  another  view  may 
be  suggested:  as  the  production  of  a  large  supply  of 
seeds  evidently  is  of  high  importance  to  many  plants, 
and  as  we  have  seen  in  the  three  foregoing  cases 

*  '  Die  Befruchtung  der  Blumen,'  pp.  319,  326. 


304:  GYNO-DICECIOUS  PLANTS.  CHAP.  VII. 

that  the  females  produce  many  more  seeds  than  the 
hermaphrodites,  increased  fertility  seems  to  me  the 
more  probable  cause  of  the  formation  and  separation  of 
the  two  forms.  From  the  data  above  given  it  follows 
that  ten  plants  of  Tliymus  serpyllum,  if  half  consisted 
of  hermaphrodites  and  half  of  females,  would  yield 
seeds  compared  with  ten  hermaphrodite  plants  in  the 
ratio  of  100  to  72.  Under  similar  circumstances  the 
ratio  with  Satureia  hortensis  (subject  to  the  doubt  from 
the  self -fertilisation  of  the  hermaphrodite)  would  be  as 
100  to  60.  Whether  the  two  forms  originated  in  cer- 
tain individuals  varying  and  producing  more  seed  than 
usual,  and  consequently  producing  less  pollen;  or  in 
the  stamens  of  certain  individuals  tending  from  some 
unknown  cause  to  abort,  and  consequently  producing 
more  seed,  it  is  impossible  to  decide;  but  in  either 
case,  if  the  tendency  to  the  increased  production  of 
seed  were  steadily  favoured,  the  result  would  be  the 
complete  abortion  of  the  male  organs.  I  shall  pres- 
ently discuss  the  cause  of  the  smaller  size  of  the  female 
corolla. 

Scabiosa  arvensis  (Dipsacese). — It  has  been  shown  by 
H.  Miiller  that  this  species  exists  in  Germany  under  an 
hermaphrodite  and  female  form.*  In  my  neighbourhood 
(Kent)  the  female  plants  do  not  nearly  equal  in  number 
the  hermaphrodites.  The  stamens  of  the  females  vary 
much  in  their  degree  of  abortion ;  in  some  plants  they  are 
quite  short  and  produce  no  pollen;  in  others  they  reach  to 
the  mouth  of  the  corolla,  but  their  anthers  are  not  half 
the  proper  size,  never  dehisce,  and  contain  but  few  pollen- 
grains,  these  being  colourless  and  of  small  diameter.  The 


*  ' Befruchtnng    der    Blumen,'  males  co-exist;    it    is,    however, 

&c.,  p.  368.     The  two  forms  occur  possible  that  he  may  have  been 

not    only    in    Germany,    but    in  deceived  by  the  flowers  being  so 

England     and     France.      Lecoq  strongly     proterandrous.       From 

('Geographic  Bot.'  1857,  torn.  vi.  what  Lecoq  says,  8.  succisa  likewise 

pp.  473,  477)  says  that  male  plants  appears  to  occur  under  two  forms 

as  well  as  hermaphrodites  and  fe-  in  France. 


CHAP.  VII.  GYNO-DKECIOUS  PLANTS.  3Q5 

hermaphrodite  flowers  are  strongly  proterandrous,  and  H. 
Miiller  shows  that,  whilst  all  the  stigmas  on  the  same  flower- 
head  are  mature  at  nearly  the  same  time,  the  stamens 
dehisce  one  after  the  other ;  so  that  there  is  a  great  excess 
of  pollen,  which  serves  to  fertilise  the  female  plants.  As 
the  production  of  pollen  by  one  set  of  plants  is  thus  ren- 
dered superfluous,  their  male  organs  have  become  more  or 
less  completely  aborted.  Should  it  be  hereafter  proved  that 
the  female  plants  yield,  as  is  probable,  more  seeds  than 
the  hermaphrodites,  I  should  be  inclined  to  extend  the  same 
view  to  this  plant  as  to  the  Labiatae.  I  have  also  observed 
the  existence  of  two  forms  in  our  endemic  8.  succisa,  and 
in  the  exotic  8.  atro-purpurea.  In  the  latter  plant,  dif- 
ferently to  what  occurs  in  8.  arvensis,  the  female  flowers, 
especially  the  larger  circumferential  ones,  are  smaller  than 
those  of  the  hermaphrodite  form.  According  to  Lecoq, 
the  female  flower-heads  of  8.  succisa  are  likewise  smaller 
than  those  of  what  he  calls  the  male  plants,  but  which  are 
probably  hermaphrodites. 

Echium  vulgar -e  (Boraginese). — The  ordinary  herma- 
phrodite form  appears  to  be  proterandrous,  and  nothing 
more  need  be  said  about  it.  The  female  differs  in  having 
a  much  smaller  corolla  and  shorter  pistil,  but  a  well-de- 
veloped stigma.  The  stamens  are  short ;  the  anthers  do  not 
contain  any  sound  pollen-grains,  but  in  their  place  yellow 
incoherent  cells  which  do  not  swell  in  water.  Some  plants 
were  in  an  intermediate  condition;  that  is,  had  one  or 
two  or  three  stamens  of  proper  length  with  perfect  an- 
thers, the  other  stamens  being  rudimentary.  In  one  such 
plant  half  of  one  anther  contained  green  perfect  pollen- 
grains,  and  the  other  half  yellowish-green  imperfect  grains. 
Both  forms  produced  seed,  but  I  neglected  to  observe 
whether  in  equal  numbers.  As  I  thought  that  the  state  of 
the  anthers  might  be  due  to  some  fungoid  growth,  I  exam- 
ined them  both  in  the  bud  and  mature  state,  but  could  find 
no  trace  of  mycelium.  In  1862  many  female  plants  were 
found;  and  in  1864,  32  plants  were  collected  in  two  locali- 
ties, exactly  half  of  which  were  hermaphrodites,  fourteen 
were  females,  and  two  in  an  intermediate  condition.  In 
1866, 15  plants  were  collected  in  another  locality,  and  these 
consisted  of  four  hermaphrodites  and  eleven  females.  I 
may  add  that  this  season  was  a  wet  one,  which  shows  that 


306  GYNO-DICECIOUS  PLANTS.  CHAP.  VIL 

the  abortion  of  the  stamens  can  hardly  be  due  to  the  dry- 
ness  of  the  sites  where  the  plants  grew,  as  I  at  one  time 
thought  probable.  Seeds  from  an  hermaphrodite  were 
sown  in  my  garden,  and  of  the  23  seedlings  raised,  one 
belonged  to  the  intermediate  form,  all  the  others  being 
hermaphrodites,  though  two  or  three  of  them  had  unusu- 
ally short  stamens.  I  have  consulted  several  botanical 
works,  but  have  found  no  record  of  this  plant  varying  in 
the  manner  here  described. 

Plantago  lanceolata  (Plantaginese). — Delpino  states 
that  this  plant  presents  in  Italy  three  forms,  which  gradu- 
ate from  an  anemophilous  into  an  entomophilous  condi- 
tion. According  to  H.  Miiller,*  there  are  only  two  forms 
in  Germany,  neither  of  which  show  any  special  adaptation 
for  insect  fertilisation,  and  both  appear  to  be  hermaphro- 
dites. But  I  have  found  in  two  localities  in  England  fe- 
male and  hermaphrodite  forms  existing  together;  and  the 
same  fact  has  been  noticed  by  others.f  The  females  are 
less  frequent  than  the  hermaphrodites;  their  stamens  are 
short,  and  their  anthers,  which  are  of  a  brighter  green 
•whilst  young  than  those  of  the  other  form,  dehisce  properly, 
yet  contain  either  no  pollen,  or  a  small  amount  of  imperfect 
grains  of  variable  size.  All  the  flower-heads  on  a  plant 
belong  to  the  same  form.  It  is  well  known  that  this  species 
is  strongly  proterogynous,  and  I  found  that  the  protruding 
stigmas  of  both  the  hermaphrodite  and  female  flowers  were 
penetrated  by  pollen-tubes,  whilst  their  own  anthers  were 
immature  and  had  not  escaped  out  of  the  bud.  Plantago 
media  does  not  present  two  forms;  but  it  appears  from 
Asa  Gray's  description,t  that  such  is  the  case  with  four 
of  the  North  American  species.  The  corolla  does  not  prop- 
erly expand  in  the  short-stamened  form  of  these  plants. 

Cnicus  Serratula  Eriophorum. — In  the  Composite, 
Cnicus  palustris  and  acaulis  are  said  by  Sir  J.  E.  Smith 
to  exist  as  hermaphrodites  and  females,  the  former  being 
the  more  frequent.  With  Serratula  tinctoria  a  regular 
gradation  may  be  followed  from  the  hermaphrodite  to  the 


*  '  Die  Befruchtunjr,'  &c.,  p.  342.  N.  United  States,'  2nd  edit.  1856, 
t  Mr.    C.    W.   Crocker  in   '  The  p.  269.     See  also  '  American  Jour- 
Gardener's  Chronicle,'  1864,  p.  294.  nal  of  Science,'  Nov.  1862,  p.  419, 
Mr.    W.  Marshall  writes  to  me  to  and  '  Proc.  American  Academy  of 
the  same  effect  from  Ely.  Science,'  Oct.  14, 1862,  p.  53. 
t  '  Manual  of  the  Botany  of  the 


CHAP.  VII.  SIZE  OF  THE  COROLLA.  307 

female  form ;  in  one  of  the  latter  plants  the  stamens  were 
so  tall  that  the  anthers  embraced  the  style  as  in  the  herma- 
phrodites, but  they  contained  only  a  few  grains  of  pollen, 
and  these  in  an  aborted  condition;  in  another  female,  on 
the  other  hand,  the  anthers  were  much  more  reduced  in 
size  than  is  usual.  Lastly,  Dr.  Dickie  has  shown  that  with 
Eriophorum  angustifolium  (Cyperaceae)  hermaphrodite 
and  female  forms  exist  in  Scotland  and  the  Arctic  regions 
both  of  which  yield  seed.* 

It  is  a  curious  fact  that  in  all  the  foregoing  po- 
lygamous, dioacious,  and  gyno-dioecious  plants  in  which 
any  difference  has  been  observed  in  the  size  of  the 
corolla  in  the  two  or  three  forms,  it  is  rather  larger  in 
the  females,  which  have  their  stamens  more  or  less  or 
quite  rudimentary,  than  in  the  hermaphrodites  or  males. 
This  holds  good  with  Euonymus,  Rhamnus  catharticus, 
Ilex,  Fragaria,  all  or  at  least  most  of  the  before-named 
Labiatse,  Scdbiosa  atro-purpurea,  and  Echium  vulgare. 
So  it  is,  according  to  Von  Mohl,  with  Cardamine 
amara,  Geranium  sylvaticum,  Myosotis,  and  Salvia. 
On  the  other  hand,  as  Von  Mohl  remarks,  when  a 
plant  produces  hermaphrodite  flowers  and  others 
which  are  males  owing  to  the  more  or  less  complete 
abortion  of  the  female  organs,  the  corollas  of  the 
males  are  not  at  all  increased  in  size,  or  only  excep- 
tionally and  in  a  slight  degree,  as  in  Acer.f  It  seems 
therefore  probable  that  the  decreased  size  of  the  female 
corollas  in  the  foregoing  cases  is  due  to  a  tendency  to 
abortion  spreading  from  the  stamens  to  the  petals.  We 
see  how  intimately  these  organs  are  related  in  double 
flowers,  in  which  the  stamens  are  readily  converted 
into  petals.  Indeed  some  botanists  believe  that  petals 
do  not  consist  of  leaves  directly  metamorphosed,  but  of 


*Sir  J.    E.   Smith,    'Transac-    of  the  Lirnisean  Society  of  Botany,' 
tionsof  the  Linnsean  Society,'  vol.     vol.  ix.  1865.  p.  161. 
xiii.  p.  599.     Dr.  Dickie,  'Journal          f  '  Bot.  Zeitung,'  1863,  p.  326. 


308  SIZE  OF  THE  COROLLA.  CHAP.  VII. 

metamorphosed  stamens.  That  the  lessened  size  of  the 
corolla  in  the  above  case  is  in  some  manner  an  indirect 
result  of  the  modification  of  the  reproductive  organs  is 
supported  by  the  fact  that  in  ETiamnus  catliarticus  not 
only  the  petals  but  the  green  and  inconspicuous  sepals 
of  the  female  have  been  reduced  in  size;  and  in  the 
strawberry  the  flowers  are  largest  in  the  males,  mid- 
sized in  the  hermaphrodites,  and  smallest  in  the  fe- 
males. These  latter  cases, — the  variability  in  the  size 
of  the  corolla  in  some  of  the  above  species,  for  instance 
in  the  common  thyme, — together  with  the  fact  that  it 
never  differs  greatly  in  size  in  the  two  forms — make 
me  doubt  much  whether  natural  selection  has  come 
into  play ; — that  is  whether,  in  accordance  with  H.  Miil- 
ler's  belief,  the  advantage  derived  from  the  polleniferous 
flowers  being  visited  first  by  insects  has  been  sufficient 
to  lead  to  a  gradual  reduction  of  the  corolla  of  the  fe- 
male. We  should  bear  in  mind  that  as  the  hermaphro- 
dite is  the  normal  form,  its  corolla  has  probably  retained 
its  original  size.*  An  objection  to  the  above  view  should 
not  be  passed  over;  namely,  that  the  abortion  of  the 
stamens  in  the  females  ought  to  have  added  through  the 
law  of  compensation  to  the  size  of  the  corolla;  and  this 
perhaps  would  have  occurred,  had  not  the  expenditure 
saved  by  the  abortion  of  the  stamens  been  directed  to  the 
female  reproductive  organs,  so  as  to  give  to  this  form 
increased  fertility. 


*  It  does  not  appear  to  me  that  serves  to  protect  their  pollen  from 

Kerner's  view  (' Die  Schutzmittel  rain.     In  the  genus  Thymus,  for 

des  Pollens,'  1873,  p.  56)    can  be  instance,  the  aborted  anthers   of 

accepted    in    the    present     roses,  the  female  are  much  better  pro- 

naniely,  that  the  larger  corolla  in  tected  than  the  perfect  ones  of  the 

the    hermaphrodites    and     males  hermaphrodite. 


CHAP.  VIII.        CLEISTOGAMIC  FLOWERS.  309 


CHAPTER  VIII. 

CLEISTOGAMIC  FLOWEBS. 

General  character  of  cleistogamic  flowers — List  of  the  genera  producing 
such  flowers,  and  their  distribution  in  the  vegetable  series — Viola, 
description  of  the  cleistogamic  flowers  in  the  several  species,  their 
fertility  compared  with  that  of  the  perfect  flowers — Oxalis  acetosella 
— O.  sensitiva,  three  forms  of  cleistogamic  flowers — Vandellia — 
Ononis — Impatiens— Drosera — Miscellaneous  observations  on  various 
other  cleistogamic  plants — Anemophilous  species  producing  cleisto- 
gamic flowers — Leersia,  perfect  flowers  rarely  developed — Summary 
and  concluding  remarks  on  the  origin  of  cleistogamic  flowers — The 
chief  conclusions  which  may  be  drawn  from  the  observations  in  this 
volume. 

IT  was  known  even  before  the  time  of  Linnaeus  that 
certain  plants  produced  two  kinds  of  flowers,  ordi- 
nary open  and  minute  closed  ones;  and  this  fact  for- 
merly gave  rise  to  warm  controversies  about  the  sexu- 
ality of  plants.  These  closed  flowers  have  been  appro- 
priately named  cleistogamic  by  Dr.  Kuhn.*  They  are 
remarkable  from  their  small  size  and  from  never  open- 
ing, so  that  they  resemble  buds;  their  petals  are  rudi- 
mentary or  quite  aborted;  their  stamens  are  often  re- 
duced in  number,  with  the  anthers  of  very  small  size, 
containing  few  pollen-grains,  which  have  remarkably 
thin  transparent  coats,  and  generally  emit  their  tubes 
whilst  still  enclosed  within  the  anther-cells ;  and,  lastly, 
the  pistil  is  much  reduced  in  size,  with  the  stigma  in 
same  cases  hardly  at  all  developed.  These  flowers  do 
not  secrete  nectar  or  emit  any  odour;  from  their  small 


*  '  Bot.  Zeitung,'  1867,  p.  65. 


310  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

size,  as  well  as  from  the  corolla  being  rudimentary,  they 
are  singularly  inconspicuous.  Consequently  insects  do 
not  visit  them;  nor  if  they  did,  could  they  find  an  en- 
trance. Such  flowers  are  therefore  invariably  self-fer- 
tilised; yet  they  produce  an  abundance  of  seed.  In  sev- 
eral cases  the  young  capsules  bury  themselves  beneath 
the  ground,  and  the  seeds  are  there  matured.  These 
flowers  are  developed  before,  or  after,  or  simultaneously 
with  the  perfect  ones.  Their  development  seems  to  be 
largely  governed  by  the  conditions  to  which  the  plants 
are  exposed,  for  during  certain  seasons  or  in  certain 
localities  only  cleistogamic  or  only  perfect  flowers  are 
produced. 

Dr.  Kuhn,  in  the  article  above  referred  to,  gives  a 
list  of  44  genera  including  species  which  bear  flowers 
of  this  kind.  To  this  list  I  have  added  some  genera, 
and  the  authorities  are  appended  in  a  foot-note.  I 
have  omitted  three  names,  from  reasons  likewise  given 
in  the  foot-note.  But  it  is  by  no  means  easy  to  de- 
cide in  all  cases  whether  certain  flowers  ought  to  be 
ranked  as  cleistogamic.  For  instance,  Mr.  Bentham 
informs  me  that  in  the  South  of  France  some  of  the 
flowers  on  the  vine  do  not  fully  open  and  yet  set 
fruit;  and  I  hear  from  two  experienced  gardeners  that 
this  is  the  case  with  the  vine  in  our  hot-houses;  but 
as  the  flowers  do  not  appear  to  be  completely  closed  it 
would  be  imprudent  to  consider  them  as  cleistogamic. 
The  flowers  of  some  aquatic  and  marsh  plants,  for 
instance  of  Ranunculus  aquatilis,  Alisma  natans, 
Subularia,  Illecebrum,  Menyanthes,  and  Euryale,* 
remain  closely  shut  as  long  as  they  are  sub- 

*Delpino,  'Sull'  Opera,  la  Dis-  Flora,' vol.  iii.  1825.  p.  157.     For 

tribuzione  dei  Sessi  nelle  Piante,'  the  behaviour  of  Menyanthos  in 

&c.  1867,  p.  30.     Subularia.   how-  Russia  see  GilHbert  in  'Act.  A  cart, 

ever,    sometimes   has  its    flowers  St.  Petersb.,'  1777.  part  ii.  p.  45. — 

fully  expanded  benenth  the  water.  On   Enrvale  '  Gardener's   Chroui- 

see  Sir   J.    E.    Smith,     'English  cle,' 1877,  p.  280. 


CHAP.  VIII.        CLEISTOGAMIC  FLOWERS.  311 

merged,  and  in  this  condition  fertilise  themselves. 
They  behave  in  this  manner,  apparently  as  a  protec- 
tion to  their  pollen,  and  produce  open  flowers  when 
exposed  to  the  air;  so  that  these  cases  seem  rather 
different  from  those  of  true  cleistogamic  flowers,  and 
have  not  been  included  in  the  list.  Again,  the  flowers 
of  some  plants  which  are  produced  very  early  or  very 
late  in  the  season  do  not  properly  expand;  and  these 
might  perhaps  be  considered  as  incipiently  cleisto- 
gamic; but  as  they  do  not  present  any  of  the  remark- 
able peculiarities  proper  to  the  class,  and  as  I  have 
not  found  any  full  record  of  such  cases,  they  are  not 
entered  in  the  list.  When,  however,  it  is  believed  on 
fairly  good  evidence  that  the  flowers  on  a  plant  in  its 
native  country  do  not  open  at  any  hour  of  the  day  or 
night,  and  yet  set  seeds  capable  of  germination,  these 
may  fairly  be  considered  as  cleistogamic,  notwith- 
standing that  they  present  no  peculiarities  of  struc- 
ture. I  will  now  give  as  complete  a  list  of  the  genera 
containing  cleistogamic  species  as  I  have  been  able  to 
collect. 

TABLE  38. 

List  of  Genera  including  Cleistogamic  Species  (chiefly 
after  Kuhri).* 


DICOTYLEDONS. 

Eritrichium  (Boraginete). 

Cuscuta  (Convolvulacese). 

Scrophularia  (Scrophularineae). 

Linaria 

Vandellia 

Cryphiacanthus  (Acanthacese). 

Eranthemum  " 


DICOTYLEDONS. 

Dsedalacanthus  (Acanthacea?). 

Dipteracanthus 

,?Echmanthera 

Euellia  , 

Lamium  (Labiatse). 

Salvia 

Oxybaphus  (Nyctagineae). 


*  I  have  omitted  Trifolium  and  appear  to  be  properly  cleistogamic. 

Arachis  from  the  list,  because  Von  Correa  de  Mello  (  Journal  Linn 

Mohl  says  ('Bot.    Zeitung,'   1863,  Soc.    Bot.'   vol     xi    1870,   p.  254) 

p       312^     that    the    flower-stems  observed    plants    of    Arachis    m 

merely  draw  the  flowers  beneath  Brazil,  and  could  never  find  such 

the  ground  and  that  these  do  not  flowers.  Plan tago  has  been  omitted 


312 


CLEISTOGAMIC  FLO  WEES.         CHAP.  VIII. 


TABLE  S3— continued. 


DICOTYLEDONS. 

Nyctaginia  (Nyctaginese). 

Stapelia  (Asclepiadse). 

Specularia  (Campanulacese). 

Campanula 

Hottonia  (Primulacese). 

Anandria  (Composites). 

Heterocarpsea  ( Crucif  erse ) . 

Viola  (Violacese). 

Helianthemum  (Cistinese). 

Lechea 

Pavonia  (Malvacese). 

Gaudichaudia  (Malpighiacese). 

Aspicarpa 

Camarea 

Janusia 

Polygala  (Polygalese). 

Impatiens  (Balsaminese). 

Oxalis  (Geraniaccse). 

Ononis  (Leguminosse). 

Parochsetus 

Chapmannia     " 

Stylosanthus    " 


DICOTYLEDONS. 

Lespedeza  (Leguminosse). 

Vicia 

Lathyrus 

Martinsia  vel  1       <i 

Neurocarpum  > 

Amphicarpsea 

Glycine 

Galactia 

Voandzeia 

Drosera  (Droseracese). 

MONOCOTYLEDONS. 

Juncus  (Juncese). 

Leersia  (Graminese). 

Hordeum 

Cryptostachys   " 

Commelina  (Commelineas). 

Monochoria  (Poutederacese). 

Schomburgkia  (Orchidse). 

Cattleya 

Epidendron 

Thelymitra  " 


because  as  far  as  I  can  discover  it 
produces  hermaphrodite  and  fe- 
male flower-heads,  but  not  cleis- 
togamic  flowers.  Krascheninikowia 
(vel  Stellaria)  has  been  omitted 
because  it  seems  very  doubtful 
from  Maximowicz'  description 
whether  the  lower  flowers  which 
have  no  petals  or  very  small  ones, 
and  barren  stamens  or  none,  are 
cleistogamic ;  the  upper  herma- 
phrodite flowers  are  said  never  to 
produce  fruit,  and  therefore  pro- 
bably act  as  males.  Moreover  in 
Stellaria  graminea,  as  Babington 
remarks  ('British  Botany,'  1851, 
p.  51),  "  shorter  and  longer  petals 
accompany  an  imperfection  of  the 
stamens  or  germen." 

I  have  added  to  the  list  the  fol- 
lowing cases :  Several  Acanthacese, 
for  which  see  J.  Scott  in  '  Journal 
ofBot.'  (London),  new  series,  vol. 
i.,  1872,  p.  161.  With  respect  to 
Salvia  see  Dr.  Ascherson  in  '  Bot. 
Zeitung,'  1871,  p.  555.  For  Oxy- 


baphus  and  Nyctaginia  see  Asa 
Gray  in  '  American  Naturalist,' 
Nov.  1873,  p.  692.  From  Dr. 
Torrey's  account  of  Hottonia  in- 
flata  ('Bull,  of  Torrey  Botan. 
Club,'  vol.  ii.  June,  1871)  it  is 
manifest  that  this  plant  produces 
true  cleistogamic  flowers.  For 
Pavonia  see  Bouch6  in  '  Sitzungs- 
berichte  d.  Gesellsch.  Natur. 
Frcunde,'  Oct.  20,  1874,  p.  90.  I 
have  added  Thelymitra,  as  from 
the  account  given  by  Mr.  Fitzger- 
ald in  his  magnificent  work  on 
'  Australian  Orchids '  it  appears 
that  the  flowers  of  this  plant  in  its 
native  home  never  open,  but  they 
do  not  appear  to  be  reduced  in 
size.  Nor  is  this  the  case  with 
the  flowers  of  certain  species  of 
Epidendron,  Cattleya.  &c.  (see 
second  edition  of  my  '  Fertilisation 
of  Orchids,'  p.  147),  which  with- 
out expanding  produce  capsules. 
It  is  therefore  doubtful  whether 
these  Orchidese  ought  to  have  been 


CHAP.  VIII.  VIOLA.  313 

The  first  point  that  strikes  us  in  considering  this  list 
of  55  genera,  is  that  they  are  very  widely  distributed 
in  the  vegetable  series.  They  are  more  common  in  the 
family  of  the  Leguminosae  than  in  any  other,  and  next 
in  order  in  that  of  the  Acanthaceae  and  Malpighiaceaa. 

A  large  number,  but  not  all  the  species,  of  certain 
genera,  as  of  Oxalis  and  Viola,  bear  eleistogamic  as  well 
as  ordinary  flowers.  A  second  point  which  deserves  no- 
tice is  that  a  considerable  proportion  of  the  genera  pro- 
duce more  or  less  irregular  flowers ;  this  is  the  case  with 
about  32  out  of  the  55  genera,  but  to  this  subject  I  shall 
recur. 

I  formerly  made  many  observations  on  eleistogamic 
flowers,  but  only  a  few  of  them  are  worth  giving,  since 
the  appearance  of  an  admirable  paper  by  Hugo  von 
Mohl,*  whose  examination  was  in  some  respects  much 
more  complete  than  mine.  His  paper  includes  also  an 
interesting  history  of  our  knowledge  on  the  subject. 

Viola  canina. — The  calyx  of  the  eleistogamic  flowers 
differs  in  no  respect  from  that  of  the  perfect  ones.  The 
petals  are  reduced  to  five  minute  scales;  the  lower  one, 
which  represents  the  lower  lip,  is  considerably  larger 
than  the  others,  but  with  no  trace  of  the  spur-like 
nectary;  its  margins  are  smooth,  whilst  those  of  the 
other  four  scale-like  petals  are  papillose.  D.  Miiller  of 
Upsala  says  that  in  the  specimens  which  he  observed 
the  petals  were  completely  aborted,  f  The  stamens  are 
very  small,  and  only  the  two  lower  ones  are  provided 
with  anthers,  which  do  not  cohere  together  as  in  the 
perfect  flowers.  The  anthers  are  minute,  with  the  two 


included  in  the  list.     From  what       *'Bot.   Zeitung,'  1863,  p.  30&- 


France  '  torn,  x.,  1863.  p.  195,  this  contains  the  first  full  and  satisfac- 

plant  appears  to  produce  cleisto-  tory  account  of  any  cleistogarmc 

pamic  flowers.  The  other  additions  flower. 
to  the  list  are  noticed  in  my  text. 


314:  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

cells  or  loculi  remarkably  distinct;  they  contain  very 
little  pollen  in  comparison  with  those  of  the  perfect 
flowers.  The  connective  expands  into  a  membranous 
hood-like  shield  which  projects  above  the  anther-cells. 
These  two  lower  stamens  have  no  vestige  of  the  curious 
appendages  which  secrete  nectar  in  the  perfect  flowers. 
The  three  other  stamens  are  destitute  of  anthers  and 
have  broader  filaments,  with  their  terminal  membra- 
nous expansions  flatter  or  not  so  hoodlike  as  those  of 
the  two  antheriferous  stamens.  The  pollen-grains  have 
remarkably  thin  transparent  coats;  when  exposed  to 
the  air  they  shrivel  up  quickly;  when  placed  in  water 
they  swell,  and  are  then  $^  of  an  inch  in  diameter, 
and  therefore  of  smaller  size  than  the  ordinary  pollen- 
grains  similarly  treated,  which  have  a  diameter  of 
^FuS4  °f  an  inch.  In  the  cleistogamic  flowers,  the 
pollen-grains,  as  far  as  I  could  see,  never  naturally  fall 
out  of  the  anther-cells,  but  emit  their  tubes  through  a 
pore  at  the  upper  end.  I  was  able  to  trace  the  tubes 
from  the  grains  some  way  down  the  stigma.  The  pistil 
is  very  short,  with  the  style  hooked,  so  that  its  ex- 
tremity, which  is  a  little  enlarged  or  funnel-shaped 
and  represents  the  stigma,  is  directed  downwards,  being 
covered  by  the  two  membranous  expansions  of  the  an- 
theriferous stamens.  It  is  remarkable  that  there  is  an 
open  passage  from  the  enlarged  funnel-shaped  extrem- 
ity to  within  the  ovarium;  this  was  evident,  as  slight 
pressure  caused  a  bubble  of  air,  which  had  been  drawn 
in  by  some  accident,  to  travel  freely  from  one  end  to 
the  other;  a  similar  passage  was  observed  by  Michalet 
in  V.  alba.  The  pistil  therefore  differs  considerably 
from  that  of  the  perfect  flower;  for  in  the  latter  it  is 
much  longer,  and  straight  with  the  exception  of  the 
rectangular  bent  stigma ;  nor  is  it  perforated  by  an  open 


CHAP.  VIII.  VIOLA.  315 

The  ordinary  or  perfect  flowers  have  been  said  by 
some  authors  never  to  produce  capsules;  but  this  is  an 
error,  though  only  a  small  proportion  of  them  do  so. 
This  appears  to  depend  in  some  cases  on  their  anthers 
not  containing  even  a  trace  of  pollen,  but  more  gener- 
ally on  bees  not  visiting  the  flowers.  I  twice  covered 
with  a  net  a  group  of  flowers,  and  marked  with  threads 
twelve  of  them  which  had  not  as  yet  expanded.  This 
precaution  is  necessary,  for  though  as  a  general  rule 
the  perfect  flowers  appear  considerably  before  the 
cleistogamic  ones,  yet  occasionally  some  of  the  latter 
are  produced  early  in  the  season,  and  their  capsules 
might  readily  be  mistaken  for  those  produced  by  the 
perfect  flowers.  Not  one  of  the  twelve  marked  perfect 
flowers  yielded  a  capsule,  whilst  others  under  the  net 
which  had  been  artificially  fertilised  produced  five 
capsules;  and  these  contained  exactly  the  same  aver- 
age number  of  seeds  as  some  capsules  from  flowers 
outside  the  net  which  had  been  fertilised  by  bees.  I 
have  repeatedly  seen  Bombus  hortorum,  lapidarius,  and 
a  third  species,  as  well  as  hive-bees,  sucking  the 
flowers  of  this  violet;  I  marked  six  which  were  thus 
visited,  and  four  of  them  produced  fine  capsules;  the 
two  others  were  gnawed  off  by  some  animal.  I  watched 
Bombus  hortorum  for  some  time,  and  whenever  it  came 
to  a  flower  which  did  not  stand  in  a  convenient  po- 
sition to  be  sucked,  it  bit  a  hole  through  the  spur-like 
nectary.  Such  ill-placed  flowers  would  not  yield  any 
seed  or  leave  descendants;  and  the  plants  bearing 
them  would  thus  tend  to  be  eliminated  through  natural 
selection. 

The  seeds  produced  by  the  cleistogamic  and  perfect 
flowers  do  not  differ  in  appearance  or  number.  On 
two  occasions  I  fertilised  several  perfect  flowers  with 
pollen  from  other  individuals,  and  afterwards  marked 


316  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

some  cleistogamic  flowers  on  the  same  plants;  and  the 
result  was  that  14  capsules  produced  by  the  perfect 
flowers  contained  on  an  average  9.85  seeds;  and  17 
capsules  from  the  cleistogamic  ones  contained  9.6-1 
seeds, — an  amount  of  difference  of  no  significance.  It 
is  remarkable  how  much  more  quickly  the  capsules 
from  the  cleistogamic  flowers  are  developed  than  those 
from  the  perfect  ones;  for  instance  several  perfect 
flowers  were  cross-fertilised  on  April  14th,  1863,  and  a 
month  afterwards  (May  15th)  eight  young  cleistogamic 
flowers  were  marked  with  threads;  and  when  the  two 
sets  of  capsules  thus  produced  were  compared  on  June 
3rd,  there  was  scarcely  any  difference  between  them 
in  size. 

Viola  odorata  (white  flowered,  single,  cultivated  va- 
riety).— The  petals  are  represented  by  mere  scales  as 
in  the  last  species;  but  differently  from  in  the  last, 
all  five  stamens  are  provided  with  diminutive  anthers. 
Small  bundles  of  pollen-tubes  were  traced  from  the 
five  anthers  into  the  somewhat  distant  stigma.  The 
capsules  produced  by  these  flowers  bury  themselves  in 
the  soil,  if  it  be  loose  enough,  and  there  mature  them- 
selves.* Lecoq  says  that  it  is  only  these  latter  cap- 
sules which  possess  elastic  valves;  but  I  think  this 
must  be  a  misprint,  as  such  valves  would  obviously  be 
of  no  use  to  the  buried  capsules,  but  would  serve  to 
scatter  the  seeds  of  the  sub-aerial  ones,  as  in  the  other 
specis  of  Viola.  It  is  remarkable  that  this  plant,  ac- 
cording to  Delpino,f  does  not  produce  cleistogamic 
flowers  in  one  part  of  Liguria,  whilst  the  perfect  flow- 
ers are  there  abundantly  fertile;  on  the  other  hand, 
cleistogamic  flowers  are  produced  by  it  near  Turin. 


*  Vaucher  says  ('  Hist.  Phys.  des  See  also  Lecoq,  'Geograph.  Bot.' 

Plantes  d'Europe,'  torn.   iii.  1844,  torn.  v.  1856,  p.  180. 

p.   309)   that  V.   Jiirta  and   cottina  f  '  Bull'   Opera,  la  Distribuzione 

likewise    bury   their    capsules.—  del  Sessi  nelle  Piante,'  1867,  p.  30. 


CHAP.VIli.  VIOLA.  317 

Another  fact  is  worth  giving  as  an  instance  of  corre- 
lated development;  I  found  on  a  purple  variety,  after 
it  had  produced  its  perfect  double  flowers,  and  whilst 
the  white  single  variety  was  bearing  its  cleistogamic 
flowers,  many  bud-like  bodies  which  from  their  posi- 
tion on  the  plant  were  certainly  of  a  cleistogamic  na- 
ture. They  consisted,  as  could  be  seen  on  bisecting 
them,  of  a  dense  mass  of  minute  scales  closely  folded 
over  one  another,  exactly  like  a  cabbage-head  in  minia- 
ture. I  could  not  detect  any  stamens,  and  in  the  place 
of  the  ovarium  there  was  a  little  central  column.  The 
doubleness  of  the  perfect  flowers  had  thus  spread  to  the 
cleistogamic  ones,  which  therefore  were  rendered  quite 
sterile. 

Viola  hirta. — The  five  stamens  of  the  cleistogamic 
flowers  are  provided,  as  in  the  last  case,  with  small 
anthers,  from  all  of  which  pollen-tubes  proceed  to  the 
stigma.  The  petals  are  not  quite  so  much  reduced 
as  in  V.  canina,  and  the  short  pistil  instead  of  being 
hooked  is  merely  bent  into  a  rectangle.  Of  several  per- 
fect flowers  which  I  saw  visited  by  hive-  and  humble- 
bees,  six  were  marked,  but  they  produced  only  two  cap- 
sules, some  of  the  others  having  been  accidentally  in- 
jured. M.  Monnier  was  therefore  mistaken  in  this  case 
as  in  that  of  V.  odorata,  in  supposing  that  the  perfect 
flowers  always  withered  away  and  aborted.  He  states 
that  the  peduncles  of  the  cleistogamic  flowers  curve 
downwards  and  bury  the  ovaries  beneath  the  soil.*  I 
may  here  add  that  Fritz  Miiller,  as  I  hear  from  his 
brother,  has  found  in  the  highlands  of  Southern  Brazil  a 
white-flowered  species  of  violet  which  bears  subterranean 
cleistogamic  flowers. 

*  These    statements    are    taken  to  the  supposed    sterility  of  the 

from  Professor  Oliver's    excellent  perfect  flowers  in  this  genus  see 

article  in  the  'Nat.  Hi*t.  Review,'  also  Timhal-La grave  in  'Bot.  Zei- 

July  1862,   p.   238.     With  respect  tung,'  1854,  p.  772. 


318  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

Viola  nana. — Mr.  Scott  sent  me  seeds  of  this  Indian 
species  from  the  Sikkim  Terai,  from  which  I  raised 
many  plants,  and  from  these  other  seedlings  during 
several  successive  generations.  They  produced  an 
abundance  of  cleistogamic  flowers  during  the  whole  of 
each  summer,  but  never  a  perfect  one.  When  Mr.  Scott 
wrote  to  me  his  plants  in  Calcutta  were  behaving  simi- 
larly, though  his  collector  saw  the  species  in  flower  in 
its  native  site.  This  case  is  valuable  as  showing  that 
we  ought  not  to  infer,  as  has  sometimes  been  done, 
that  a  species  does  not  bear  perfect  flowers  when  grow- 
ing naturally,  because  it  produces  only  cleistogamic 
flowers  under  culture.  The  calyx  of  these  flowers  is 
sometimes  formed  of  only  three  sepals;  two  being 
actually  suppressed  and  not  merely  coherent  with  the 
others;  this  occurred  with  five  out  of  thirty  flowers 
which  were  examined  for  this  purpose.  The  petals  are 
represented  by  extremely  minute  scales.  Of  the  sta- 
mens, two  bear  anthers  which  are  in  the  same  state  as 
in  the  previous  species,  but,  as  far  as  I  could  judge, 
each  of  the  two  cells  contained  only  from  20  to  25  deli- 
cate transparent  pollen-grains.  These  emitted  their 
tubes  in  the  usual  manner.  The  three  other  stamens 
bore  very  minute  rudimentary  anthers,  one  of  which  was 
generally  larger  than  the  other  two,  but  none  of  them 
contained  any  pollen.  In  one  instance,  however,  a  sin- 
gle cell  of  the  larger  rudimentary  anther  included  a 
little  pollen.  The  style  consists  of  a  short  flattened  tube, 
somewhat  expanded  at  its  upper  end,  and  this  forms  an 
open  channel  leading  into  the  ovarium,  as  described 
under  V.  canina.  It  is  slightly  bent  towards  the  two 
fertile  anthers. 

Viola  Roxburghiana. — This  species  bore  in  my  hot- 
house during  two  years  a  multitude  of  cleistogamic 
flowers,  which  resembled  in  all  respects  those  of  the 


CHAP.  VIII.  VIOLA.  319 

last  species;  but  no  perfect  ones  were  produced.  Mr. 
Scott  informs  me  that  in  India  it  bears  perfect  flowers 
only  during  the  cold  season,  and  that  these  are  quite 
fertile.  During  the  hot,  and  more  especially  during 
the  rainy  season,  it  bears  an  abundance  of  cleistogamic 
flowers. 

Many  other  species,  besides  the  five  now  described, 
produce  cleistogamic  flowers;  this  is  the  case,  accord- 
ing to  D.  Miiller,  Michalet,  Von  Mohl,  and  Hermann 
Miiller,  with  V.  elatior,  lancifolia,  sylvatica,  palustris, 
mirabilis,  bicolor,  ionodium,  and  biflora.  But  V.  tri- 
color does  not  produce  them. 

Michalet  asserts  that  V.  palustris  produces  near 
Paris  only  perfect  flowers,  which  are  quite  fertile;  but 
that  when  the  plant  grows  on  mountains  cleistogamic 
flowers  are  produced ;  and  so  it  is  with  V.  biflora.  The 
same  author  states  that  he  has  seen  in  the  case  of  V.  alba 
flowers  intermediate  in  structure  between  the  perfect 
and  cleistogamic  ones.  According  to  M.  Boisduval,  an 
Italian  species,  V.  Ruppii,  never  bears  in  France  "  des 
fleurs  bien  apparentes,  ce  qui  ne  1'empeche  pas  de  fruc- 
tifier." 

It  is  interesting  to  observe  the  gradation  in  the 
abortion  of  the  parts  in  the  cleistogamic  flowers  of 
the  several  foregoing  species.  It  appears  from  the  state- 
ments by  D.  Miiller  and  Von  Mohl  that  in  V.  mirabilis 
the  calyx  does  not  remain  quite  closed;  all  five  stamens 
are  provided  with  anthers,  and  some  pollen-grains  prob- 
ably fall  out  of  the  cells  on  the  stigma,  instead  of  pro- 
truding their  tubes  whilst  still  enclosed,  as  in  the  other 
species.  In  V.  hirta  all  five  stamens  are  likewise  an- 
theriferous ;  the  petals  are  not  so  much  reduced  and  the 
pistil  not  so  much  modified  as  in  the  following  species. 
In  V.  nana  and  elatior  only  two  of  the  stamens  properly 
bear  anthers,  but  sometimes  one  or  even  two  of  the  others 


320  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

are  thus  provided.  Lastly,  in  V.  canina  never  more 
than  two  of  the  stamens,  as  far  as  I  have  seen,  bear 
anthers;  the  petals  are  much  more  reduced  than  in  V. 
hirta,  and  according  to  D.  Miiller  are  sometimes  quite 
absent. 

Oxalis  acetosella. — The  existence  of  cleistogamic 
flowers  on  this  plant  was  discovered  by  Michalet.* 
They  have  been  fully  described  by  Von  Mohl,  and  I 
can  add  hardly  anything  to  his  description.  In  my 
specimens  the  anthers  of  the  five  longer  stamens  were 
nearly  on  a  level  with  the  stigmas;  whilst  the  smaller 
and  less  plainly  bilobed  anthers  of  the  five  shorter 
stamens  stood  considerably  below  the  stigmas,  so  that 
their  tubes  had  to  travel  some  way  upwards.  Ac- 
cording to  Michalet  these  latter  anthers  are  sometimes 
quite  aborted.  In  one  case  the  tubes,  which  ended  in 
excessively  fine  points,  were  seen  by  me  stretching  up- 
wards from  the  lower  anthers  towards  the  stigmas, 
which  they  had  not  as  yet  reached.  My  plants  grew 
in  pots,  and  long  after  the  perfect  flowers  had  with- 
ered they  produced  not  only  cleistogamic  but  a  few 
minute  open  flowers,  which  were  in  an  intermediate  con- 
dition between  the  two  kinds.  In  one  of  these  the  pol- 
len-tubes from  the  lower  anthers  had  reached  the  stig- 
mas, though  the  flower  was  open.  The  footstalks  of 
the  cleistogamic  flowers  are  much  shorter  than  those 
of  the  perfect  flowers,  and  are  so  much  'bowed  down- 
wards that  they  tend,  according  to  Von  Mohl,  to  bury 
themselves  in  the  moss  and  dead  leaves  on  the  ground. 
Michalet  also  says  that  they  are  often  hypogean.  In 
order  to  ascertain  the  number  of  seeds  produced  by  these 
flowers,  I  marked  eight  of  them;  two  failed,  one  cast 
its  seed  abroad,  and  the  remaining  five  contained  on  an 


*  '  Bull.  Soc.  Bot.  de  France,'  torn.  vii.  1860,  p.  465. 


CHAP.  VIII.  OXALIS.  321 

average  10.0  seeds  per  capsule.  This  is  rather  above 
the  average  9.2,  which  eleven  capsules  from  perfect 
flowers  fertilised  with  their  own  pollen  yielded,  and  con- 
siderably above  the  average  7.9,  from  the  capsules  of 
perfect  flowers  fertilised  with  pollen  from  another  plant ; 
but  this  latter  result  must,  I  think,  have  been  ac- 
cidental. 

Hildebrand,  whilst  searching  various  Herbaria,  ob- 
served that  many  other  species  of  Oxalis  besides  0. 
acetosella  produce  cleistogamic  flowers ;  *  and  I  hear 
from  him  that  this  is  the  case  with  the  heterostyled  tri- 
morphic  0.  incarnata  from  the  Cape  of  Good  Hope. 

Oxalis  (Biophytum)  sensitiva. — This  plant  is  ranked 
by  many  botanists  as  a  distinct  genus,  but  as  a  sub- 
genus  by  Bentham  and  Hooker.  Many  of  the  early 
flowers  on  a  mid-styled  plant  in  my  hot-house  did  not 
open  properly,  and  were  in  an  intermediate  condition 
between  cleistogamic  and  perfect.  Their  petals  varied 
from  a  mere  rudiment  to  about  half  their  proper  size; 
nevertheless  they  produced  capsules.  I  attributed 
their  state  to  unfavourable  conditions,  for  later  in  the 
season  fully  expanded  flowers  of  the  proper  size  ap- 
peared. But  Mr.  Thwaites  afterwards  sent  me  from 
Ceylon  a  number  of  long-styled,  mid-styled,  and  short- 
styled  flower-stalks  preserved  in  spirits;  and  on  the 
same  stalks  with  the  perfect  flowers,  some  of  which 
were  fully  expanded  and  others  still  in  bud,  there  were 
small  bud-like  bodies  containing  mature  pollen,  but 
with  their  calyces  closed.  These  cleistogamic  flowers 
do  not  differ  much  in  structure  from  the  perfect  ones 
of  the  corresponding  form,  with  the  exception  that 
their  petals  are  reduced  to  extremely  minute,  barely 
visible  scales,  which  adhere  firmly  to  the  rounded 


1  Monatsbericlit  der  Akad.  der  Wiss.  zu  Berlin,'  1866,  p.  369. 


322  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

bases  of  the  shorter  stamens.  Their  stigmas  are  much 
less  papillose,  and  smaller  in  about  the  ratio  of  13  to 
20  divisions  of  the  micrometer,  as  measured  trans- 
versely from  apex  to  apex,  than  the  stigmas  of  the 
perfect  flowers.  The  styles  are  furrowed  longitudinally, 
and  are  clothed  with  simple  as  well  as  glandular  hairs, 
but  only  in  the  cleistogamic  flowers  produced  by  the 
long-styled  and  mid-styled  forms.  The  anthers  of  the 
longer  stamens  are  a  little  smaller  than  the  correspond- 
ing ones  of  the  perfect  flowers,  in  about  the  ratio  of 
11  to  14.  They  dehisce  properly,  but  do  not  appear 
to  contain  much  pollen.  Many  pollen-grains  were 
attached  by  short  tubes  to  the  stigmas;  but  many 
others,  still  adhering  to  the  anthers,  had  emitted 
their  tubes  to  a  considerable  length,  without  having 
come  in  contact  with  the  stigmas.  Living  plants 
ought  to  be  examined,  as  the  stigmas,  at  least  of  the 
long-styled  form,  project  beyond  the  calyx,  and  if 
visited  by  insects  (which,  however,  is  very  improbable) 
might  be  fertilised  with  pollen  from  a  perfect  flower. 
The  most  singular  fact  about  the  present  species  is 
that  long-styled  cleistogamic  flowers  are  produced  by 
the  long-styled  plants,  and  mid-styled  as  well  as 
short-styled  cleistogamic  flowers  by  the  other  two 
forms;  so  that  there  are  three  kinds  of  cleistogamic 
and  three  kinds  of  perfect  flowers  produced  by  this 
one  species !  Most  of  the  heterostyled  species  of 
Oxalis  are  more  or  less  sterile,  many  absolutely  so,  if 
illegitimately  fertilised  with  their  own-form  pollen.  It 
is  therefore  probable  that  the  pollen  of  the  cleisto- 
gamic flowers  has  been  modified  in  power,  so  as  to  act 
on  their  own  stigmas,  for  they  yield  an  abundance  of 
seeds.  We  may  perhaps  account  for  the  cleiostogamic 
flowers  consisting  of  the  three  forms,  through  the  prin- 
ciple of  correlated  growth,  by  which  the  cleistogamic 


CHAP.  VIII.  VANDELLIA.  323 

flowers    of    the    double    violet    have    been    rendered 
double. 

Vandellia  nummularifolia. — Dr.  Kuhn  has  col- 
lected *  all  the  notices  with  respect  to  cleistogamic 
flowers  in  this  genus,  and  has  described  from  dried  spe- 
cimens those  produced  by  an  Abyssinian  species.  Mr. 
Scott  sent  me  from  Calcutta  seeds  of  the  above  com- 
mon Indian  weed,  from  which  many  plants  were  succes- 
sively raised  during  several  years.  The  cleistogamic 
flowers  are  very  small,  being  when  fully  mature  under 
sV  of  an  inch  (1.27  mm.)  in  length.  The  calyx  does 
not  open,  and  within  it  the  delicate  transparent  corolla 
remains  closely  folded  over  the  ovarium.  There  are 
only  two  anthers  instead  of  the  normal  number  of  four, 
and  their  filaments  adhere  to  the  corolla.  The  cells  of 
the  anthers  diverge  much  at  their  lower  ends  and  are 
only  Tj-jj-g-  of  an  inch  (.181  mm.)  in  their  longer  diameter. 
They  contain  but  few  pollen-grains,  and  these  emit 
their  tubes  whilst  still  within  the  anther.  The  pistil 
is  very  short,  and  is  surmounted  by  a  bilobed  stigma. 
As  the  ovary  grows  the  two  anthers  together  with  the 
shrivelled  corolla,  all  attached  by  the  dried  pollen- 
tubes  to  the  stigma,  are  torn  off  and  carried  upwards 
in  the  shape  of  a  little  cap.  The  perfect  flowers  gener- 
ally appear  before  the  cleistogamic,  but  sometimes 
simultaneously  with  them.  During  one  season  a  large 
number  of  plants  produced  no  perfect  flowers.  It  has 
been  asserted  that  the  latter  never  yield  capsules;  but 
this  is  a  mistake,  as  they  do  so  even  when  insects  are 
excluded.  Fifteen  capsules  from  cleistogamic  flowers 
on  plants  growing  under  favourable  conditions  con- 
tained on  an  average  64.2  seeds,  with  a  maximum  of 
87;  whilst  20  capsules  from  plants  growing  much 


'Bot.  Zcitung,' 1867,  p.  65. 


324  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

crowded  yielded  an  average  of  only  48.  Sixteen  cap- 
sules from  perfect  flowers  artificially  crossed  with  pol- 
len from  another  plant  contained  on  an  average  93 
seeds,  with  a  maximum  of  137.  Thirteen  capsules  from 
self -fertilised  perfect  flowers  gave  an  average  of  62  seeds, 
with  a  maximum  of  135.  Therefore  the  capsules  from 
the  cleistogamic  flowers  contained  fewer  seeds  than 
those  from  perfect  flowers  when  cross-fertilised,  and 
slightly  more  than  those  from  perfect  flowers  self-fer- 
tilised. 

Dr.  Kuhn  believes  that  the  Abyssinian  V.  sessiflora 
does  not  differ  specifically  from  the  foregoing  species. 
But  its  cleistogamic  flowers  apparently  include  four  an- 
thers instead  of  two  as  above  described.  The  plants, 
moreover,  of  V.  sessiflora  produce  subterranean  runners 
which  yield  capsules;  and  I  never  saw  a  trace  of  such 
runners  in  V.  nummularifolia,  although  many  plants 
were  cultivated. 

Linaria  spuria. — Michalet  says  *  that  short,  thin, 
twisted  branches  are  developed  from  the  buds  in  the 
axils  of  the  lower  leaves,  and  that  these  bury  them- 
selves in  the  ground.  They  there  produce  flowers  not 
offering  any  peculiarity  in  structure,  excepting  that 
their  corollas,  though  properly  coloured,  are  deformed. 
These  flowers  may  perhaps  be  ranked  as  cleistogamic, 
as  they  are  developed,  and  not  merely  drawn,  beneath 
the  ground. 

Ononis  columns. — Plants  were  raised  from  seeds 
sent  me  from  Northern  Italy.  The  sepals  of  the 
cleistogamic  flowers  are  elongated  and  closely  pressed 
together;  the  petals  are  much  reduced  in  size',  colour- 
less, and  folded  over  the  interior  organs.  The  fila- 
ments of  the  ten  stamens  are  united  into  a  tube,  and 


*  'Bull.  Soc.  Bot.  de  France,'  torn.  vii.  I860,  p.  468. 


CHAP.  VIII.  ONONIS.  325 

this  is  not  the  case,  according  to  Von  Mohl,  with  the 
cleistogamic  flowers  of  other  Leguminosse.  Five  of 
the  stamens  are  destitute  of  anthers,  and  alternate  with 
the  five  thus  provided.  The  two  cells  of  the  anthers 
are  minute,  rounded  and  separated  from  one  another 
by  connective  tissue ;  they  contain  but  few  pollen-grains, 
and  these  have  extremely  delicate  coats.  The  pistil  is 
hook-shaped,  with  a  plainly  enlarged  stigma,  which  is 
curled  down,  towards  the  anthers;  it  therefore  differs 
much  from  that  of  the  perfect  flower.  During  the  year 
1867  no  perfect  flowers  were  produced,  but  in  the  fol- 
lowing year  there  were  both  perfect  and  cleistogamic 
ones. 

Ononis  minutissima. — My  plants  produced  both  per- 
fect and  cleistogamic  flowers;  but  I  did  not  examine 
the  latter.  Some  of  the  former  were  crossed  with  pollen 
from  a  distinct  plant,  and  six  capsules  thus  obtained 
yielded  on  an  average  3.66  seeds,  with  a  maximum  of 
5  in  one.  Twelve  perfect  flowers  were  marked  and  al- 
lowed to  fertilise  themselves  spontaneously  under  a  net, 
and  they  yielded  eight  capsules,  containing  on  an  av- 
erage 2.38  seeds,  with  a  maximum  of  3  in  one.  Fifty- 
three  capsules  produced  by  the  cleistogamic  flowers  con- 
tained on  an  average  4.1  seeds,  so  that  these  were  the 
most  productive  of  all;  and  the  seeds  themselves  looked 
finer  even  than  those  from  the  crossed  perfect  flowers. 
According  to  Mr.  Bentham,  0.  parviflora  likewise  bears 
cleistogamic  flowers ;  and  he  informs  me  that  these  flow- 
ers are  produced  by  all  three  species  early  in  the  spring ; 
whilst  the  perfect  ones  appear  afterwards,  and  therefore 
in  a  reversed  order  compared  with  those  of  Viola  and 
Oxalis.  Some  of  the  species,  for  instance  Ononis  co- 
lumnce,  bear  a  fresh  crop  of  cleistogamic  flowers  in  the 
autumn. 

Latliyrus  nissolia  apparently  offers  a  case  of  the  first 


326  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

stage  in  the  production  of  cleistogamic  flowers,  for  on 
plants  growing  in  a  state  of  nature,  many  of  the  flowers 
never  expand  and  yet  produce  fine  pods.  Some  of  the 
buds  are  so  large  that  they  seem  on  the  point  of  expan- 
sion; others  are  much  smaller,  but  none  so  small  as  the 
true  cleistogamic  flowers  of  the  foregoing  species.  As 
I  marked  these  buds  with  thread  and  examined  them 
daily,  there  could  be  no  mistake  about  their  producing 
fruit  without  having  expanded. 

Several  other  Leguminous  genera  produce  cleisto- 
gamic flowers,  as  may  be  seen  in  the  previous  list;  but 
much  does  not  appear  to  be  known  about  them.  Von 
Mohl  says  that  their  petals  are  commonly  rudimentary, 
that  only  a  few  of  their  anthers  are  developed,  their 
filaments  are  not  united  into  a  tube  and  their  pistils 
are  hook-shaped.  In  three  of  the  genera,  namely  Vicia, 
Amphicarpaea,  and  Voandzeia,  the  cleistogamic  flowers 
are  produced  on  subterranean  stems.  The  perfect  flow- 
ers of  Voandzeia,  which  is  a  cultivated  plant,  are  said 
never  to  produce  fruit ;  *  but  we  should  remember  how 
often  fertility  is  affected  by  cultivation. 

Impatiens  fulva. — Mr.  A.  W.  Bennett  has  published 
an  excellent  description,  with  figures,  of  this  plant,  f 
He  shows  that  the  cleistogamic  and  perfect  flowers 
differ  in  structure  at  a  very  early  period  of  growth,  so 
that  the  existence  of  the  former .  cannot  be  due  merely 
to  the  arrested  development  of  the  latter, — a  conclusion 
which  indeed  follows  from  most  of  the  previous  de- 
scriptions. Mr.  Bennett  found  on  the  banks  of  the  Wey 
that  the  plants  which  bore  cleistogamic  flowers  alone 
were  to  those  bearing  perfect  flowers  as  20  to  1;  but 


*  Cornea    de    Mello     ('Journal  African  plant,  which  is  sometimes 

Linn.  Soc.  Bot.'  vol.  xi.  1870,  p.  cultivated  in  Brazil. 

254)  particularly  attended  to  the  t  'Journal  Linn.  Soc.  Bot.'  vol. 

flowering    and    fruiting    of   this  xiii.  1872,  p.  147. 


CHAP.  VIII.  IMPATIENS.  327 

we  should  remember  that  this  is  a  naturalised  species. 
The  perfect  flowers  are  usually  barren  in  England ;  but 
Professor  Asa  Gray  writes  to  me  that  after  midsummer 
in  the  United  States  some  or  many  of  them  produce 
capsules. 

Impatiens  noli-me-tangere. — I  can  add  nothing  of 
importance  to  Von  Mohl's  description,  excepting  that 
one  of  the  rudimentary  petals  shows  a  vestige  of  a 
nectary,  as  Mr.  Bennett  likewise  found  to  be  the  case 
with  /.  fulva.  As  in  this  latter  species  all  five  stamens 
produce  some  pollen,  though  small  in  amount;  a 
single  anther  contains,  according  to  Yon  Mohl,  not 
more  than  50  grains,  and  these  emit  their  tubes 
while  still  enclosed  within  it.  The  pollen-grains  of 
the  perfect  flowers  are  tied  together  by  threads,  but 
not,  so  far  as  I  could  see,  those  of  the  cleistogamic 
flowers;  and  a  provision  of  this  kind  would  here  have 
been  useless,  as  the  grains  can  never  be  transported 
by  insects.  The  flowers  of  /.  balsamina  are  visited  by 
humble-bees,*  and  I  am  almost  sure  that  this  is  the  case 
with  the  perfect  flowers  of  I.  noli-me-langere.  From 
the  perfect  flowers  of  this  latter  species  covered  with 
a  net  eleven  spontaneously  self-fertilised  capsules  were 
produced,  and  these  yielded  on  an  average  3.45  seeds. 
Some  perfect  flowers  with  their  anthers  still  containing 
an  abundance  of  pollen  were  fertilised  with  pollen  from 
a  distinct  plant;  and  the  three  capsules  thus  produced 
contained,  to  my  surprise,  only  2,  2,  and  1  seed.  As 
7.  balsamina  is  proterandrous,  so  probably  is  the  pres- 
ent species ;  and  if  so,  cross-fertilisation  was  effected  by 
me  at  too  early  a  period,  and  this  may  account  for  the 
capsules  yielding  so  few  seeds. 

Drosera  rotundifolia. — The  first  flower-stems  which 


H.  Miiller,  '  Die  Befruchtung,'  &c.  p.  170. 


328  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

were  thrown  up  by  some  plants  in  my  green-house 
bore  only  cleistogamie  flowers.  The  petals  of  small 
size  remained  permanently  closed  over  the  repro- 
ductive organs,  but  their  white  tips  could  just  be 
seen  between  the  almost  completely  closed  sepals. 
The  pollen,  which  was  scanty  in  amount,  but  not  so 
scanty  as  in  Viola  or  Oxalis,  remained  enclosed 
within  the  anthers,  whence  the  tubes  proceeded  and 
penetrated  the  stigma.  As  the  ovarium  swelled  the 
little  withered  corolla  was  carried  upwards  in  the 
form  of  a  cap.  These  cleistogamie  flowers  produced 
an  abundance  of  seed.  Later  in  the  season  perfect 
flowers  appeared.  With  plants  in  a  state  of  nature  the 
flowers  open  only  in  the  early  morning,  as  I  have  been 
informed  by  Mr.  Wallis,  who  particularly  attended  to 
the  time  of  their  flowering.  In  the  case  of  D.  Anglica, 
the  still  folded  petals  on  some  plants  in  my  green- 
house opened  just  sufficiently  to  leave  a  minute 
aperture;  the  anthers  dehisced  properly,  but  the 
pollen-grains  adhered  in  a  mass  to  them,  and  thence 
emitted  their  tubes,  which  penetrated  the  stigmas. 
These  flowers,  therefore,  were  in  an  intermediate  con- 
dition, and  could  not  be  called  either  perfect  or  cleis- 
togamie. 

A  few  miscellaneous  observations  may  be  added  with 
respect  to  some  other  species,  as  throwing  light  on  our 
subject.  Mr.  Scott  states  *  that  Eranthemum  ambi- 
guum  bears  three  kinds  of  flowers, — large,  conspicuous, 
open  ones,  which  are  quite  sterile — others  of  interme- 
diate size,  which  are  open  and  moderately  fertile — and 
lastly  small  closed  or  cleistogamie  ones  which  are  per- 
fectly fertile.  Ruellia  tuberosa,  likewise  one  of  the 
Acanthaceae,  produces  both  open  and  cleistogamie  flow- 


*  '  Journal  of  Botany,'  London,  new  series,  vol.  i.  1872,  pp.  161-4. 


CHAP.  VIII.        CLEISTOGAMIC  FLOWERS.  329 

ers;  the  latter  yield  from  18  to  24,  whilst  the  former 
only  from  8  to  10  seeds;  these  two  kinds  of  flowers 
are  produced  simultaneously,  whereas  in  several  other 
members  of  the  family  the  cleistogamie  ones  appear 
only  during  the  hot  season.  According  to  Torrey  and 
Gray,  the  North  American  species  of  Helianthemum, 
when  growing  in  poor  soil,  produce  only  cleistogamie 
flowers.  The  cleistogamie  flowers  of  Specularia  per- 
foliata  are  highly  remarkable,  as  they  are  closed  by  a 
tympanum  formed  by  the  rudimentary  corolla,  and  with- 
out any  trace  of  an  opening.  The  stamens  vary  from 
3  to  5  in  number,  as  do  the  sepals.*  The  collecting 
hairs  on  the  pistil,  which  play  so  important  a  part  in 
the  fertilisation  of  the  perfect  flowers  are  here  quite 
absent.  Sir  J.  Hooker  and  Dr.  Thomson  state  f  that 
some  of  the  Indian  species  of  Campanula  produce  two 
kinds  of  flowers ;  the  smaller  ones  being  borne  on  longer 
peduncles  with  differently  formed  sepals,  and  produc- 
ing a  more  globose  ovary.  The  flowers  are  closed  by 
a  tympanum  like  that  in  Specularia.  Some  of  the  plants 
produce  both  kinds  of  flowers,  others  only  one  kind; 
both  yield  an  abundance  of  seeds.  Professor  Oliver 
adds  that  he  has  seen  flowers  on  Campanula  colorata  in 
an  intermediate  condition  between  cleistogamie  and  per- 
fect ones. 

The  solitary  almost  sessile  cleistogamie  flowers  pro- 
duced by  Monochoria  vaginalis  are  differently  protected 
from  those  in  any  of  the  previous  cases,  namely  within 
"  a  short  sack  formed  of  the  membranous  spathe,  with- 
out any  opening  or  fissure."  There  is  only  a  single 


*Von    Mohl,     'Bot.     Zeitung,'  of  the    perfect  flower    is    mostly 

1863,  pp.  314  and  323.     Dr.   Brom-  5-cleft. 

field    rPhytologist,'   vol.   iii.    p.  f  Journal  Lmn.  Soc.'    vol.   11. 

530)  also  remarks  that  the  calyx  1857,    p.    7.     See    also   Professor 

of    the    cleistogamie    flowers    is  Oliver    in    'Nat.   Hist.    Review,' 

usually   only  3-cleft,    while  that  1862,  p.  240. 
23 


330  CLEISTOGAMIC  FLOWERS.        CHAP.  VIII. 

fertile  stamen;  the  style  is  almost  obsolete,  with  the 
three  stigmatic  surfaces  directed  to  one  side.  Both  the 
perfect  and  cleistogamic  flowers  produce  seeds.* 

The  cleistogamic  flowers  on  some  of  the  Mal- 
pighiaceae  seem  to  be  more  profoundly  modified  than 
those  in  any  of  the  foregoing  genera.  According  to 
A.  de  Jussieu  f  they  are  differently  situated  from  the 
perfect  flowers;  they  contain  only  a  single  stamen,  in- 
stead of  5  or  6;  and  it  is  a  strange  fact  that  this 
particular  stamen  is  not  developed  in  the  perfect 
flowers  of  the  same  species.  The  style  is  absent  or 
rudimentary;  and  there  are  only  two  ovaries  instead 
of  three.  Thus  these  degraded  flowers,  as  Jussieu 
remarks,  "  laugh  at  our  classifications,  for  the  greater 
number  of  the  characters  proper  to  the  species,  to  the 
genus,  to  the  family,  to  the  class  disappear."  The 
calyces  of  the  perfect  flowers  are  studded  with  glands, 
and  their  absence  on  the  cleistogamic  flowers  may  prob- 
ably be  explained  by  an  observation  of  Fritz  Miiller, 
who  informs  me  that  in  the  one  species,  Bunchosia 
Oaudichaudiana,  the  fertilisation  of  which  he  has  often 
witnessed,  the  perfect  flowers  are  regularly  visited  by 
bees  belonging  to  the  genera  Tetrapedia  and  Epicharis. 
These  bees  sit  down  on  the  flowers,  gnawing  the 
glands  on  the  outside  of  the  calyx,  and  in  doing 
so  the  under  sides  of  their  bodies  are  dusted  with 
pollen,  by  which  afterwards  other  flowers  are  ferti- 
lised. Such  visits  to  the  cleistogamic  flowers  would  be 
useless. 

As  the  Asclepiadous  genus  Stapelia  is  said  to  pro- 
duce cleistogamic  flowers,  the  following  case  may  be 
worth  giving.  I  have  never  heard  of  the  perfect  flowers 
of  Hoya  carnosa  setting  seeds  in  this  country,  but  some 


*  Dr.  Kirk,  'Jour.  Linn.  Soc.,'         f 'Archives  dn  Museum.'  trim. 
vol.  viii.  1864,  p.  147.  iii.  1843,  pp.  35-38,  82-86,  589,  598. 


CHAP.  VIII.         CLEISTOGAMIC  FLOWERS.  331 

capsules  were  produced  in  Mr.  Farrer's  hot-house;  and 
the  gardener  detected  that  they  were  the  product  of 
minute  bud-like  bodies,  three  or  four  of  which  could 
sometimes  be  found  on  the  same  umbel  with  the  perfect 
flowers.  They  were  quite  closed  and  hardly  thicker 
than  their  peduncles.  The  sepals  presented  nothing 
particular,  but  internally  and  alternating  with  them, 
there  were  five  small  flattened  heart-shaped  papillae,  like 
rudiments  of  petals;  but  the  homological  nature  of 
which  appeared  doubtful  to  Mr.  Bentham  and  Dr. 
Hooker.  No  trace  of  anthers  or  of  stamens  could  be 
detected ;  and  I  knew  from  having  examined  many  cleis- 
togamic  flowers  what  to  look  for.  There  were  two 
ovaries,  full  of  ovules,  quite  open  at  their  upper  ends, 
with  their  edges  festooned,  but  with  no  trace  of  a  proper 
stigma.  In  all  these  flowers  one  of  the  two  ovaries 
withered  and  blackened  long  before  the  other.  The  one 
perfect  capsule,  3|  inches  in  length,  which  was  sent  me, 
had  likewise  been  developed  from  a  single  carpel.  This 
capsule  contained  an  abundance  of  plumose  seeds,  many 
of  which  appeared  quite  sound,  but  they  did  not  ger- 
minate when  sown  at  Kew.  Therefore  the  little 
bud-like  flower  which  produced  this  capsule  prob- 
ably was  as  destitute  of  pollen  as  were  those  which  I 
examined. 

Juncus  Ijufonius  and  Hordeum. — All  the  species 
hitherto  mentioned  which  produce  cleistogamic  flow- 
ers are  entomophilous ;  but  Juncus  and  seven  genera 
of  Gramineae  are  anemophilous.  Juncus  lufonius  is  re- 
markable *  by  bearing  in  parts  of  Kussia  only  cleisto- 
gamic flowers,  which  contain  three  instead  of  the  six 
anthers  found  in  the  perfect  flowers.  In  the  genus 


*  See  Dr.  Ascherson's  interesting  paper  in  '  Bot.  Zeitung,'  1871,  p. 
551.    Also  1872,  p.  697. 


332  CLEISTOGAMIC  FLOWERS.         CHAP.  VIII. 

Hordeum  it  has  been  shown  by  Delpino  *  that  the  ma- 
jority of  the  flowers  are  cleistogamic,  some  of  the  others 
expanding  and  apparently  allowing  of  cross-fertilisa- 
tion. I  hear  from  Fritz  Miiller  that  there  is  a  grass 
in  Southern  Brazil,  in  which  the  sheath  of  the  upper- 
most leaf,  half  a  metre  in  length,  envelopes  the  whole 
panicle;  and  this  sheath  never  opens  until  the  self- 
fertilised  seeds  are  ripe.  On  the  roadside  some  plants 
had  been  cut  down,  whilst  the  cleistogamic  panicles 
were  developing,  and  these  plants  afterwards  produced 
free  or  unenclosed  panicles  of  small  size,  bearing  per- 
fect flowers. 

Leersia  oryzoides. — It  has  long  been  known  that 
this  plant  produces  cleistogamic  flowers,  but  these  were 
first  described  with  care  by  M.  Duval-Jouve.f  I  pro- 
cured plants  from  a  stream  near  Eeigate,  and  cultivated 
them  for  several  years  in  my  green-house.  The  cleis- 
togamic flowers  are  very  small,  and  usually  mature  their 
seeds  within  the  sheaths  of  the  leaves.  These  flowers 
are  said  by  Duval-Jouve  to  be  filled  by  slightly  viscid 
fluid;  but  this  was  not  the  case  with  several  that  I 
opened;  but  there  was  a  thin  film  of  fluid  between  the 
coats  of  the  glumes,  and  when  these  were  pressed  the 
fluid  moved  about,  giving  a  singularly  deceptive  ap- 
pearance of  the  whole  inside  of  the  flower  being  thus 
filled.  The  stigma  is  very  small  and  the  filaments  ex- 
tremely short;  the  anthers  are  less  than  -gV  of  an  inch 
in  length,  or  about  one-third  of  the  length  of  those 
in  the  perfect  flowers.  One  of  the  three  anthers  de- 
hisces before  the  two  others.  Can  this  have  any  rela- 
tion with  the  fact  that  in  some  other  species  of  Leersia 


*  '  Bollettini  del  Comizio  agrario  Hordeum,  in  '  Monatebericht  d.  K. 

Parmense.'     Marzo  e  Aprile,  1871.  Akad.  Berlin,'  Oct.  1872,  p.  7GO. 

An  abstract  of  this  valuable  paper  f  'Bull.    Bot.   Soc.   de   France,' 

is  given  in  'Bot.  Zeitnng,'  1871.  torn.  x.  1863,  p.  194. 
p.  537.     See  also  Hildebrand  on 


CHAP.  VIII.  LEERSIA.  333 

only  two  stamens  are  fully  developed  ?  *  The  anthers 
shed  their  pollen  on  the  stigma;  at  least  in  one  in- 
stance this  was  clearly  the  case,  and  by  tearing  open 
the  anthers  under  water  the  grains  were  easily  detached. 
Towards  the  apex  of  the  anthers  the  grains  are  arranged 
in  a  single  row  and  lower  down  in  two  or  three  rows, 
so  that  they  could  be  counted;  and  there  were  about  35 
in  each  cell,  or  70  in  the  whole  anther;  and  this  is  an 
astonishingly  small  number  for  an  anemophilous  plant. 
The  grains  have  very  delicate  coats,  are  spherical  and 
about  in^nj-  of  an  inch  (.0181  mm.),  whilst  those  of  the 
perfect  flowers  are  about  ^fa  of  an  inch  (.0254  mm.) 
in  diameter. 

M.  Duval-Jouv.e  states  that  the  panicles  very  rarely 
protrude  from  their  sheaths,  but  that  when  this  does 
happen  the  flowers  expand  and  exhibit  well-developed 
ovaries  and  stigmas,  together  with  full-sized  anthers 
containing  apparently  sound  pollen;  nevertheless  such 
flowers  are  invariably  quite  sterile.  Schreiber  had  pre- 
viously observed  that  if  a  panicle  is  only  half  protruded, 
this  half  is  sterile,  whilst  the  still  included  half  is  fer- 
tile. Some  plants  which  grew  in  a  large  tub  of  water 
in  my  green-house  behaved  on  one  occasion  in  a  very 
different  manner.  They  protruded  two  very  large  much- 
branched  panicles;  but  the  florets  never  opened,  though 
these  included  fully  developed  stigmas  and  stamens 
supported  on  long  filaments  with  large  anthers  that 
dehisced  properly.  If  these  florets  had  opened  for  a 
short  time  unperecived  by  me  and  had  then  closed  again, 
the  empty  anthers  would  have  been  left  dangling  out- 
side. Nevertheless  they  yielded  on  August  17th  an 
abundance  of  fine  ripe  seeds.  Here  then  we  have  a  near 
approach  to  the  single  case  as  yet  known  f  of  this  grass 

*  Asa  Gray,  '  Manual  of  Bot.  of       t  Dr.  Ascherson,  '  Bot.  Zcitung,' 
United  States,'  1856,  p.  540.  1884,  p.  350. 


334  CONCLUDING  REMARKS  CHAP.  VIII. 

producing  in  a  state  of  nature  (in  Germany)  perfect 
flowers  which  yielded  a  copious  supply  of  fruit.  Seeds 
from  the  cleistogamic  flowers  were  sent  by  me  to 
Mr.  Scott  in  Calcutta,  who  there  cultivated  the  plants 
in  various  ways,  but  they  never  produced  perfect 
flowers. 

In  Europe  Leersia  oryzoides  is  the  sole  representa- 
tive of  its  genus,  and  Duval-Jouve,  after  examining  sev- 
eral exotic  species,  found  that  it  apparently  is  the  sole1 
one  which  bears  cleistogamic  flowers.  It  ranges  from 
Persia  to  North  America,  and  specimens  from  Pennsyl- 
vania resembled  the  European  ones  in  their  concealed 
manner  of  fructification.  There  can  therefore  be  little 
doubt  that  this  plant  generally  propagates  itself  through- 
out an  immense  area  by  cleistogamic  seeds,  and  that 
it  can  hardly  ever  be  invigorated  by  cross-fertilisation. 
It  resembles  in  this  respect  those  plants  which  are 
now  widely  spread,  though  they  increase  solely  by  a  sex- 
ual generation.* 

Concluding  remarks  on  Cleistogamic  Flowers. — 
That  these  flowers  owe  their  structure  primarily  to  the 
arrested  development  of  perfect  ones,  we  may  infer  from 
such  cases  as  that  of  the  lower  rudimentary  petal  in 
Viola  being  larger  than  the  others,  like  the  lower  lip 
of  the  perfect  flower, — from  a  vestige  of  a  spur  in  the 
cleistogamic  flowers  of  Impatiens, — from  the  ten  sta- 
mens of  Ononis  being  united  into  a  tube, — and  other 
such  structures.  The  same  inference  may  be  drawn 
from  the  occurrence,  in  some  instances,  on  the  same 
plant  of  a  series  of  gradations  between  the  cleistogamic 
and  perfect  flowers.  But  that  the  former  owe  their 
origin  wholly  to  arrested  development  is  by  no  means 
the  case ;  for  various  parts  have  been  specially  modified, 


*  T  have  collected  several  snch     mestication.'  ch.  xviii. — 2nd  edit, 
cases  in  my  '  Variation  under  Do-     vol.  ii.  p.  153. 


CHAP.  VIII.     ON  CLEISTOGAMIC  FLOWEKS.  335 

so  as  to  aid  in  the  self-fertilisation  of  the  flowers,  and 
as  a  protection  to  the  pollen;  for  instance,  the  hook- 
shaped  pistil  in  Viola  and  in  some  other  genera,  by 
which  the  stigma  is  brought  close  to  the  fertile  anthers, 
— the  rudimentary  corolla  of  Specularia  modified  into 
a  perfectly  closed  tympanum,  and  the  sheath  of  Mono- 
choria  modified  into  a  closed  sack, — the  excessively  thin 
coats  of  the  pollen-grains, — the  anthers  not  being  all 
equally  aborted,  and  other  such  cases.  Moreover  Mr. 
Bennett  has  shown  that  the  buds  of  the  cleistogamic  and 
perfect  flowers  of  Impatiens  differ  at  a  very  early  period 
of  growth. 

The  degree  to  which  many  of  the  most  important 
organs  in  these  degraded  flowers  have  been  reduced 
or  even  wholly  obliterated,  is  one  of  their  most  re- 
markable peculiarities,  reminding  us  of  many  parasitic 
animals.  In  some  cases  only  a  single  anther  is  left, 
and  this  contains  but  few  pollen-grains  of  diminished 
size;  in  other  cases  the  stigma  has  disappeared, 
leaving  a  simple  open  passage  into  the  ovarium.  It 
is  also  interesting  to  note  the  complete  loss  of  trifling 
points  in  the  structure  or  functions  of  certain  parts, 
which  though  of  service  to  the  perfect  flowers,  are  of 
none  to  the  cleistogamic;  for  instance,  the  collecting 
hairs  on  the  pistil  of  Specularia,  the  glands  on  the 
calyx  of  the  Malpighiacese,  the  nectar-secreting  ap- 
pendages to  the  lower  stamens  of  Viola,  the  secretion 
of  nectar  by  other  parts,  the  emission  of  a  sweet  odour, 
and  apparently  the  elasticity  of  the  valves  in  the 
buried  capsules  of  Viola  odorata.  We  here  see,  as 
throughout  nature,  that  as  soon  as  any  part  or  char- 
acter becomes  superfluous  it  tends  sooner  or  later  to 
disappear. 

Another  peculiarity  in  these  flowers  is  that  the 
pollen-grains  generally  emit  their  tubes  whilst  still 


336  CONCLUDING  REMARKS  CHAP.  VIIL 

enclosed  within  the  anthers;  but  this  is  not  so  re- 
markable a  fact  as  was  formerly  thought,  when  the 
case  of  Asclepias  was  alone  known.*  It  is,  however, 
a  wonderful  sight  to  behold  the  tubes  directing  them- 
selves in  a  straight  line  to  the  stigma,  when  this 
is  at  some  little  distance  from  the  anthers.  As  soon 
as  they  reach  the  stigma  or  the  open  passage  leading 
into  the  ovarium,  no  do"ubt  they  penetrate  it,  guided 
by  the  same  means,  whatever  these  may  be,  as  in  the 
case  of  ordinary  flowers.  I  thought  that  they  might 
be  guided  by  the  avoidance  of  light :  some  pollen-grains 
of  a  willow  were  therefore  immersed  in  an  extremely 
weak  solution  of  honey,  and  the  vessel  was  placed 
so  that  the  light  entered  only  in  one  direction,  lat- 
erally or  from  below  or  from  above,  but  the  long 
tubes  were  in  each  case  protruded  in  every  possible 
direction. 

As  cleistogamic  flowers  are  completely  closed  they 
are  necessarily  self-fertilised,  not  to  mention  the  ab- 
sence of  any  attraction  to  insects :  and  they  thus 
differ  widely  from  the  great  majority  of  ordinary 
flowers.  Delpino  believes  f  that  cleistogamic  flowers 
have  been  developed  in  order  to  ensure  the  production 
of  seeds  under  climatic  or  other  conditions  which  tend 
to  prevent  the  fertilisation  of  the  perfect  flowers.  I  do 
not  doubt  that  this  holds  good  to  a  certain  limited  ex- 
tent, but  the  production  of  a  large  supply  of  seeds  with 
little  consumption  of  nutrient  matter  or  expenditure  of 


*  The  case  of  Asclepias  was  de-  emission  of  the  tubes  from  the 

scribed  by  E.  Brown.     Baillon  as-  pollen-masses  while    still    within 

serts  ( '  Adansonia,'  torn.  ii.  1862,  the  anthers,  in  three  widely  dis- 

p.  58)  that  with  many  plants  the  tinct   Orchidean  genera,   namely 

tubes   are    emitted    from   pollen-  Aceras,  Malaxis,  and  Neottia :  see 

grains  which  have  not  come  into  '  The    Various     Contrivances    by 

contact  with  the  stigma  ;  and  that  which  Orchids  are  Fertilised,'  2nd 

they  may  be  seen  advancing  hori-  edit.,  p.  258. 

zontally  through  the  air  towards  t  '  Sull'    Opera  la  Distribuzione 

the  stigma.     I  have  observed  the  dei  Sessi  nello  Piante,'  18t>7,  p.  30. 


CHAP.  VIII.     ON  CLEISTOGAMIC  FLOWERS.  337 

vital  force  is  probably  a  far  more  efficient  motive  power. 
The  whole  flower  is  much  reduced  in  size:  but  what  is 
much  more  important,  an  extremely  small  quantity  of 
pollen  has  to  be  formed,  as  none  is  lost  through  the 
action  of  insects  or  the  weather;  and  pollen  contains 
much  nitrogen  and  phosphorus.  Von  Mohl  estimated 
that  a  single  cleistogamic  anther-cell  of  Oxalis  aceto- 
sella  contained  from  one  to  two  dozen  pollen-grains ;  we 
will  say  20,  and  if  so  the  whole  flower  can  have  produced 
at  most  400  grains;  with  Impatiens  the  whole  number 
may  be  estimated  in  the  same  manner  at  250;  with 
Leersia  at  210 ;  and  with  Viola  nana  at  only  100.  These 
figures  are  wonderfully  low  compared  with  the  243,600 
pollen-grains  produced  by  a  flower  of  Leontodon,  the 
4,863  by  an  Hibiscus,  or  the  3,654,000  by  a  Paeony.* 
We  thus  see  that  cleistogamic  flowers  produce  seeds  with 
a  wonderfully  small  expenditure  of  pollen;  and  they 
produce  as  a  general  rule  quite  as  many  seeds  as  the 
perfect  flowers. 

That  the  production  of  a  large  number  of  seeds  is 
necessary  or  beneficial  to  many  plants  needs  no  evi- 
dence. So  of  course  is  their  preservation  before  they 
are  ready  for  germination;  and  it  is  one  of  the  many 
remarkable  peculiarities  of  the  plants  which  bear 
cleistogamic  flowers,  that  an  incomparably  larger  pro- 
portion of  them  than  of  ordinary  plants  bury  their 
young  ovaries  in  the  ground; — an  action  which  it 
may  be  presumed  serves  to  protect  them  -from  being 
devoured  by  birds  or  other  enemies.  But  this  advan- 
tage is  accompanied  by  the  loss  of  the  power  of  wide 
dissemination.  !S!"o  less  than  eight  of  the  genera 
in  the  list  at  the  beginning  of  this  chapter  include 
species  which  act  in  this  manner,  namely,  several 

*  The  an tli ori ties  for  these  statements  are  given  in  my  '  Effects  of 
Cross  and  Self-Fertilisation,'  p.  376. 


338  CONCLUDING  REMARKS  CHAP.  VIII. 

kinds  of  Viola,  Oxalis,  Vandellia,  Linaria,  Commelina, 
and  at  least  three  genera  of  Leguminosae.  The  seeds 
also  of  Leersia,  though  not  buried,  are  concealed  in 
the  most  perfect  manner  within  the  sheaths  of  the 
leaves.  Cleistogamic  flowers  possess  great  facilities 
for  burying  their  young  ovaries  or  capsules,  owing  to 
their  small  size,  pointed  shape,  closed  condition,  and 
the  absence  of  a  corolla;  and  we  can  thus  understand 
how  it  is  that  so  many  of  them  have  acquired  this  cu- 
rious habit. 

It  has  already  been  shown  that  in  about  33  out  of 
the  67  genera  in  the  list  just  referred  to,  the  perfect 
flowers  are  irregular;  and  this  implies  that  they  have 
been  specially  adapted  for  fertilisation  by  insects. 
Moreover  three  of  the  genera  with  regular  flowers  are 
adapted  by  other  means  for  the  same  end.  Flowers 
thus  constructed  are  liable  during  certain  seasons  to 
be  imperfectly  fertilised,  namely,  when  the  proper 
insects  are  scarce;  and  it  is  difficult  to  avoid  the 
belief  that  the  production  of  cleistogamic  flowers, 
which  ensures  under  all  circumstances  a  full  supply 
of  seed,  has  been  in  part  determined  by  the  perfect 
flowers  being  liable  to  fail  in  their  fertilisation.  But 
if  this  determining  cause  be  a  real  one,  it  must  be  of 
subordinate  importance,  as  eight  of  the  genera  in  the 
list  are  fertilised  by  the  wind;  and  there  seems  no 
reason  why  their  perfect  flowers  should  fail  to  be 
fertilised  more  frequently  than  those  in  any  other 
anemophilous  genus.  In  contrast  with  what  we  here 
see  with  respect  to  the  large  proportion  of  the  perfect 
flowers  being  irregular,  one  genus  alone  out  of  the  38 
heterostyled  genera  described  in  the  previous  chapters 
bears  such  flowers;  yet  all  these  genera  are  absolutely 
dependent  on  insects  for  their  legitimate  fertilisation. 
I  know  not  how  to  account  for  this  difference  in  the 


CHAP.  VIII.     ON  CLEISTOGAMIC  FLOWERS.  339 

proportion  of  the  plants  bearing  regular  and  irregular 
flowers  in  the  two  classes,  unless  it  be  that  the  hetero- 
styled  flowers  are  already  so  well  adapted  for  cross-fer- 
tilisation, through  the  position  of  their  stamens  and 
pistils  and  the  difference  in  power  of  their  two  or  three 
kinds  of  pollen,  that  any  additional  adaptation,  namely, 
through  the  flowers  being  made  irregular,  has  been  ren- 
dered superfluous. 

Although  cleistogamic  flowers  never  fail  to  yield 
a  large  number  of  seeds,  yet  the  plants  bearing  them 
usually  produce  perfect  flowers,  either  simultaneously 
or  more  commonly  at  a  different  period;  and  these 
are  adapted  for  or  admit  of  cross-fertilisation.  From 
the  cases  given  of  the  two  Indian  species  of  Viola, 
which  produced  in  this  country  during  several  years 
only  cleistogamic  flowers,  and  of  the  numerous  plants 
of  Vandellia  and  of  some  plants  of  Ononis  which  be- 
haved during  one  whole  season  in  the  same  manner, 
it  appears  rash  to  infer  from  such  cases  as  that  of 
Salvia  cleistogama  not  having  produced  perfect  flowers 
during  five  years  in  Germany,*  and  of  an  Aspicarpa 
not  having  done  so  during  several  years  in  Paris,  that 
these  plants  would  not  bear  perfect  flowers  in  their 
native  homes.  Von  Mohl  and  several  other  botanists 
have  repeatedly  insisted  that  as  a  general  rule  the 
perfect  flowers  produced  by  cleistogamic  plants  are 
sterile;  but  it  has  been  shown  under  the  head  of  the 
several  species  that  this  is  not  the  case.  The  perfect 
flowers  of  Viola  are  indeed  sterile  unless  they  are  vis- 
ited by  bees;  but  when  thus  visited  they  yield  the  full 
number  of  seeds.  As  far  as  I  have  been  able  to  dis- 
cover there  is  only  one  absolute  exception  to  the  rule 
that  the  perfect  flowers  are  fertile,  namely,  that  of 


*  Dr.  Ascherson,  'Bot.  Zeit.,'  1871,  p.  555. 


3iO  CONCLUDING  REMARKS  CHAP.  VIII. 

Voandzeia;  and  in  this  case  we  should  remember  that 
cultivation  often  affects  injuriously  the  reproductive  or- 
gans. Although  the  perfect  flowers  of  Leersia  some- 
times yield  seeds,  yet  this  occurs  so  rarely,  as  far  as 
hitherto  observed,  that  it  practically  forms  a  second  ex- 
ception to  the  rule. 

As  cleistogamic  flowers  are  invariably  fertilised,  and 
as  they  are  produced  in  large  numbers,  they  yield  al- 
together a  much  larger  supply  of  seeds  than  do  the  per- 
fect flowers  on  the  same  plant.  But  the  latter  flowers 
will  occasionally  be  cross-fertilised,  and  their  offspring 
will  thus  be  invigorated,  as  we  may  infer  from  a  wide- 
spread analogy.  But  of  such  invigoration  I  have  only 
a  small  amount  of  direct  evidence :  two  crossed  seed- 
lings of  Ononis  minutissima  were  put  into  competition 
with  two  seedlings  raised  from  cleistogamic  flowers; 
they  were  at  first  all  of  equal  height;  the  crossed  were 
then  slightly  beaten;  but  on  the  following  year  they 
showed  the  usual  superiority  of  their  class,  and  were  to 
the  self-fertilised  plants  of  cleistogamic  origin  as  100 
to  88  in  mean  height.  With  Vandellia  twenty  crossed 
plants  exceeded  in  height  twenty  plants  raised  from 
cleistogamic  seeds  only  by  a  little,  namely,  in  the  ratio 
of  100  to  94. 

It  is  a  natural  inquiry  how  so  many  plants  belong- 
ing to  various  very  distinct  families  first  came  to  have 
the  development  of  their  flowers  arrested,  so  as  ulti- 
mately to  become  cleistogamic.  That  a  passage  from 
the  one  state  to  the  other  is  far  from  difficult  is  shown 
by  the  many  recorded  cases  of  gradations  between  the 
two  states  on  the  same  plant,  in  Viola,  Oxalis,  Biophy- 
tum,  Campanula,  &c.  In  the  several  species  of  Viola 
the  various  parts  of  the  flowers  have  also  been  modified 
in  very  different  degrees.  Those  plants  which  in  their 
own  country  produce  flowers  of  full  or  nearly  full  size, 


CHAP.  VIII.     ON  CLEISTOGAMIC  FLOWERS.  341 

but  never  expand  (as  with  Thelymitra),  and  yet  set 
fruit,  might  easily  be  rendered  eleistogamic.  Lathyrus 
nissolia  seems  to  be  in  an  incipient  transitional  state, 
as  does  Drosera  Anglica,  the  flowers  of  which  are  not 
perfectly  closed.  There  is  good  evidence  that  flowers 
sometimes  fail  to  expand  and  are  somewhat  reduced 
in  size,  owing  to  exposure  to  unfavourable  conditions, 
but  still  retain  their  fertility  unimpaired.  Linnaeus 
observed  in  1753  that  the  flowers  on  several  plants 
brought  from  Spain  and  grown  at  TJpsala  did  not 
show  any  corolla  and  yet  produced  seeds.  Asa  Gray 
has  seen  flowers  on  exotic  plants  in  the  Northern  United 
States  which  never  expanded  and  yet  fruited.  With 
certain  English  plants,  which  bear  flowers  during  near- 
ly the  whole  year,  Mr.  Bennett  found  that  those  pro- 
duced during  the  winter  season  were  fertilised  in  the 
bud;  whilst  with  other  species  having  fixed  times  for 
flowering,  but  "  which  had  been  tempted  by  a  mild  Janu- 
ary to  put  forth  a  few  wretched  flowers,"  no  pollen  was 
discharged  from  the  anthers,  and  no  seed  was  formed. 
The  flowers  of  Lysimachia  vulgaris  if  fully  exposed 
to  the  sun  expand  properly,  while  those  growing  in 
shady  ditches  have  smaller  corollas  which  open  only 
slightly;  and  these  two  forms  graduate  into  one  an- 
other in  intermediate  stations.  Herr  Bouche's  obser- 
vations are  of  especial  interest,  for  he  shows  that  both 
temperature  and  the  amount  of  light  affect  the  size  of 
the  corolla;  and  he  gives  measurements  proving  that 
with  some  plants  the  corolla  is  diminished  by  the  in- 
creasing cold  and  darkness  of  the  changing  season,  whilst 
with  others  it  is  diminished  by  the  increasing  heat  and 
light.* 

*  For  the  statement  by  Linnseus,  xxxix.  1865.  p.  105.     Bennett  in 

Bee  Mohl  in  'Bot.  Zeitung,'  1863,  'Nature,'   Nov.  1869,  p.  11.    The 

S327        \sa    Gray,    '  American  Rev.  G.  Henslow  also  says  (   (jflr- 

ournal  of  Science, '2nd  series,  vol.  dener's  Chronicle,'  1877,   p.  271; 


342  CONCLUDING  REMARKS  CHAP.  VIII. 

The  belief  that  the  first  step  towards  flowers  being 
rendered  cleistogamic  was  due  to  the  conditions  to  which 
they  were  exposed,  is  supported  by  the  fact  of  various 
plants  belonging  to  this  class  either  not  producing 
their  cleistogamic  flowers  under  certain  conditions,  or, 
on  the  other  hand,  producing  them  to  the  complete  ex- 
clusion of  the  perfect  ones.  Thus  some  species  of  Viola 
do  not  bear  cleistogamic  flowers  when  growing  on  the 
lowlands  or  in  certain  districts.  Other  plants  when 
cultivated  have  failed  to  produce  perfect  floAvers  during 
several  successive  years;  and  this  is  the  case  with  Jun- 
cus  bufonius  in  its  native  land  of  Eussia.  Cleistogamic 
flowers  are  produced  by  some  species  late  and  by  others 
early  in  the  season;  and  this  agrees  with  the  view  that 
the  first  step  towards  their  development  was  due  to  cli- 
mate; though  the  periods  at  which  the  two  sorts  of 
flowers  now  appear  must  since  have  become  much  more 
distinctly  defined.  We  do  not  know  whether  too  low 
or  too  high  a  temperature  or  the  amount  of  light  acts 
in  a  direct  manner  on  the  size  of  the  corolla,  or  indi- 
rectly, through  the  male  organs  being  first  affected. 
However  this  may  be,  if  a  plant  were  prevented  either 
early  or  late  in  the  season  from  fully  expanding  its 
corolla,  with  some  reduction  in  its  size,  but  with  no 
loss  of  the  power  of  self-fertilisation,  then  natural  se- 
lection might  well  complete  the  work  and  render  it 
strictly  cleistogamic.  The  various  organs  would  also, 
it  is  probable,  be  modified  by  the  peculiar  conditions 
to  which  they  are  subjected  within  a  completely  closed 
flower;  also  by  the  principle  of  correlated  growth,  and 
by  the  tendency  in  all  reduced  organs  finally  to  disap- 


also    'Nature,'    Oct.   19,    1876,   p.  ers  are  self-fertilised.    On  Lysima- 

543)     "that    when    the     autumn  rhia,   H.    Muller,   'Nature,'    Sept. 

draws  on,  and  habitually  in  win-  1873,  p.  433.      Bouche,   '  Sitzungrs- 

ter  for  such  of  our  wild  flowers  as  hnricht  der  (resell.     Naturforsch. 

blossom  at  that  season,"  the  flow-  Freunde,'  Oct.  1874,  p.  90. 


CHAP.  VIII.     ON  CLEISTOGAMIC  FLOWERS.  343 

pear.  The  result  would  be  the  production  of  cleisto- 
gamic  flowers  such  as  we  now  see  them;  and  these  are 
admirably  fitted  to  yield  a  copious  supply  of  seed  at  a 
wonderfully  small  cost  to  the  plant. 

I  wilt  now  sum  up  very  briefly  the  chie'f  conclusions 
which  seem  to  follow  from  the  observations  given  in 
this  volume.  Cleistogamic  flowers  afford,  as  just  stated, 
an  abundant  supply  of  seeds  with  little  expenditure; 
and  we  can  hardly  doubt  that  they  have  had  their  struc- 
ture modified  and  degraded  for  this  special  purpose; 
perfect  flowers  being  still  almost  always  produced  so 
as  to  allow  of  occasional  cross-fertilisation.  Herma- 
phrodite plants  have  often  been  rendered  monoecious, 
dioecious  or  polygamous;  but  as  the  separation  of  the 
sexes  would  have  been  injurious,  had  not  pollen  been  al- 
ready transported  habitually  by  insects,  or  by  the  wind 
from  flower  to  flower,  we  may  assume  that  the  process 
of  separation  did  not  commence  and  was  not  completed 
for  the  sake  of  the  advantages  to  be  gained  from  cross- 
fertilisation.  The  sole  motive  for  the  separation  of  the 
sexes  which  occurs  to  me,  is  that  the  production  of  a 
great  number  of  seeds  might  become  superfluous  to  a 
plant  under  changed  conditions  of  life;  and  it  might 
then  be  highly  beneficial  to  it  that  the  same  flower  or 
the  same  individual  should  not  have  its  vital  powers 
taxed,  under  the  struggle  for  life  to  which  all  organisms 
are  subjected,  by  producing  both  pollen  and  seeds. 
With  respect  to  the  plants  belonging  to  the  gyno-dice- 
cious  sub-class,  or  those  which  co-exist  as  hermaphrodites 
and  females,  it  has  been  proved  that  they  yield  a  much 
larger  supply  of  seeds  than  they  would  have  done  if 
they  had  all  remained  hermaphrodites ;  and  we  may  feel 
sure  from  the  large  number  of  seeds  produced  by  many 
plants  that  such  production  is  often  necessary  or  ad- 


344  GENERAL  CONCLUSIONS.          CHAP.  VIII. 

vantageous.  It  is  therefore  probable  that  the  two  forms 
in  this  sub-class  have  been  separated  or  developed  for 
this  special  end. 

Various  hermaphrodite  plants  have  become  hetero- 
styled,  and  now  exist  under  two  or  three  forms;  and 
we  may  confidently  believe  that  this  has  been  effected 
in  order  that  cross-fertilisation  should  be  assured.  For 
the  full  and  legitimate  fertilisation  of  these  plants  pollen 
from  the  one  form  must  be  applied  to  the  stigma  of  an- 
other. If  the  sexual  elements  belonging  to  the  same 
form  are  united  the  union  is  an  illegitimate  one  and 
more  or  less  sterile.  With  dimorphic  species  two  ille- 
gitimate unions,  and  with  trimorphic  species  twelve 
are  possible.  There  is  reason  to  believe  that  the  ster- 
ility of  these  unions  has  not  been  specially  acquired, 
but  follows  as  an  incidental  result  from  the  sexual  ele- 
ments of  the  two  or  three  forms  having  been  adapted  to 
act  on  one  another  in  a  particular  manner,  so  that  any 
other  kind  of  union  is  inefficient,  like  that  between  dis- 
tinct species.  Another  and  still  more  remarkable  inci- 
dental result  is  that  the  seedlings  from  an  illegitimate 
union  are  often  dwarfed  and  more  or  less  or  completely 
barren,  like  hybrids  from  the  union  of  two  widely  dis- 
tinct species. 


INDEX. 


ACANTHACE^. 

COBYLXTS. 

A. 

Boragineie,  101. 

Boreau  on  cowslip  and  primrose, 

Acanthaceie,  312. 

57. 

Acer  campestre,  12,  307. 

Borreria,  127. 

Adoxa,  9. 

Bouch6  on  Pavonia,  312  ;  effect  of 

^giphila  elata,  124. 

temperature  and  light  on  corolla, 

mollis,  124. 

341. 

obdurata,  124,  286. 

Bouvardia  leianiha,  135. 

Alefeld,  Dr.,  on  Linum,  100. 

Braun  on  Dracocephalum,  298. 

Alisma  natans,  310. 

Breitenbach,  W.,  on  Primula  ela* 

Amphicarpsea,  326. 

lior,  34,  272. 

Amsinckia  spectabilis,   110;   varia- 

Bromfield,  Dr.,  on  primrose  and 

bility  in  length  of  stamens  and 

cowslip,  57  ;  Primula  elatior,  73  ; 

pistil,  262,  267. 

Specularia  perfoliata,  329. 

Anchusa  arvensis,  111. 

Brown,  Eobert,  on  sexual  changes, 

Androsace  vitalliana,  53. 
Anthers,  size  of,  in  different  forms, 

282. 
Buckwheat,  the  common,  111. 

253  ;  contabescent,  283. 

Arachis,  311. 

Arnebia  hispidissima,  111. 

C. 

Ascherson,  Dr.,   on  Salvia  deisto- 

gama,  312,  339  ;  Juncus  bufonins, 

Cattha  palustris,  13. 

332  ;  Leersia  oryzoides,  333. 

Campanula  colorata,  329. 

Asclepias,  336. 

Cardamine  amara,  307. 

Ash,  the  common,  11. 

Caspary,  Prof.,  on  Rhamnus  cathar- 

Asperula  scoparia,  284. 

ticus,  293. 

Axell  on  Primula  strieta,  50. 

Cattleya,  312. 

Chamissoa,  291. 

Cinchona  micrantha,  134. 

B. 

Cleistogamic  flowers,  309;   list  of 

genera,   311  ;    on  their   origin, 

Babington,  Prof.,  on  Primula  ela- 

342. 

tior,  72  ;  fitellaria  graminea,  312. 

Cnicus  acaulis,  306. 

Baillon,  emission  of  the  tubes  from 
pollen-grains,  336. 

palustris,  306. 
Coccocifpselurn,   133;   pollen-grains 

Belhomme,  M.,  on  ray-florets,  6. 

of,  251. 

Bennett,  A.  W.,  on  Impatiens  fulva, 
326  ;  flowers  fertilised  whilst  in 
the  bud  state,  341. 

Coprosma,  285. 
Cordia,  117  ;  pistil  of,  254. 
Corolla,  difference  in  size  in  the 

Bentham,  Mr.,  on  the  differentia- 

sexes of  the  same  species,  307, 

tion  of  the  sexes,  11. 

308. 

Bentham,  Mr.,  on  the  cleistogamic 

Corydalis,  146. 

flowers  of  Ononis,  325. 

Corylus  avellana,  10. 

24                                                                345 

346 


INDEX. 


COWSLIP. 

GYNO-DKECIOUS. 

Cowslip,  the  common,  14  ;  short- 

Euonymus  Europseus,  287-292. 

ana  long-styled,  19-22,  56-71. 

Euphrasia  offieinalis,  4. 

Cratoxylon  formosum,  123. 

Euryale,  310. 

Crocker,  C.  W.,  on  Plantago  lanceo- 

lata,  306. 

F. 

Cryptostachys,  312. 

Ctiphea  purpurea,  168. 

Faramea,  129  ;  pollen-grains,  129. 

, 

Fitzgerald,  Mr.,  on  Tlielymitra,  312. 

Forsythia  suspensa,   117  ;  stamens, 

D. 

253. 

viridissima,  117. 

Darwin,  Charles,  on  reproductive 

Fragaria  Chiloensis,  292. 

organs  under  cultivation,  7  ;  in- 

  elatior,  293. 

tercrossed  plants,  30  ;  prepotency 

vesca,  292. 

of  pollen,  62  ;  insects  fertilising, 

Virginiana,  292. 

flowers,  79  ;  Cephalanthera  gran- 
diflora,  98  ;  Epidendron  and   Cat- 

Fraxinus  excelsior,  11. 

tleya,    313  ;    number  of  pollen- 

grains,  337. 

G. 

,  W.,  on  Pulmonaria  angusti- 

folia,  105,  107. 

Galium  cruciatum,  286. 

Datura  arborea,  252. 

Gartner  on  the  sterility  of  unions 

Delpino,  plants  fertilised  by  the 

between    distinct    species,    29  ; 

wind,  10  ;  on  the  walnut,   10  ; 

Primula  vulgaris  and    veris,   58, 

Polygonacese,   114;  pollen-grains, 

59  ;  hybrid    Verbascums,    76,    77, 

251  ;    Thymus     serpyllum,     299  ; 

80  ;  prepotency  of  pollen,   242  ; 

closed    or   cleistogamic  flowers, 

variation  in  the  sexual  powers 

310,  336  ;   Viola  odorata,  316. 

of  plants,  268  ;  contabescent  an- 

Dianthus barbatiis,  30. 

thers,  193,  283. 

Dickie,  Dr.,  on  Eriophorum  angus- 

Gentianeie,  115. 

tifolium,  307. 

Geraniacese,  168. 

Dictamnus  fraxinetta,  146. 
Diodia,  135. 
Dioecious  and  sub-dioecious  plants, 

Geranium  syhaticum,  307. 
Gesneria  pendulina,  262. 
Gilia  aggregata,  118. 

287. 

coronopifolia,  119. 

Discospermum,  286. 

micrantha,  119. 

Doubleday,  H.,  on  Primula  elatior, 

nudicaulis,  119. 

73. 

pulchella,  118. 

Dracocephalum  Moldavicum,  298. 
Drosera  Anqlica,  328,  341. 
rotundlfolia,  327. 

Gillibert  on  Menyanthes,  310. 
Gloriosa  lily,  the,  146. 
Godron  on  hybrid  Primulas,  55. 

Duval-Jouve,  M.,  on  Cryptostachys, 
313  ;  Lcersia  oryzoides,  332,  333. 

Gray,  Prof.  Asa,  proposes  the  term 
heterogone  or  heterogonous,  2  ;  on 

Dyer,   Thiselton,   on    Salma  Hor- 

Linum,  101  ;  Leucosmia  Burnetti- 

minum,  8  ;  Cratoxylon  formosum, 

ana   and    acuminata,   114;    For- 

123. 

sythia  suspensa,    117  ;  Gilia  pul- 

chella, 118  ;  G.  coronopifolia,  119  ; 

E. 

Phlox    subulata,    120  ;    Mitchella 

repens,  125  ;  heterostyled  plants, 

Echium  vulgare,  111,  305,  307. 
Epidendron,  312. 

245  ;  Coprosma,   285  ;  Euonymus, 
287  ;   Rhamnus    lanceolatus,    295, 

Epigssa  repens,  296. 

296  ;    Epigtea   repens,   296  ;    Ilex 

Equal-styled  vars.  of  Primula,  273. 

opaca,  298  ;  Plantago  media,  306  ; 

Eranthemum  ambiguum,  328. 

Oxybaphus  and  Nyctaginia,  312  ; 

Eriophorum  angu'sti  folium,  307. 

impatiens    fulva,    327  ;     Leersia, 

Erythroxylum,    121  ;   pollen-grains 
of,  251. 

333  ;  cleistofjamic  flowers,  341. 
Gyno-dicecious  plants,  298. 

INDEX. 


34? 


Hart,  Mr.,  on  Nepeta  glechoma, 
300. 

Hautbois  Strawberry,  the,  293. 

Hedyotis,  133. 

Henslow,  Eev.  Prof.,  on  hybrid 
Primulse,  61. 

Henslow,  Ecv.  G.,  on  flowers  self- 
fertilised  during  the  winter,  341. 

Herbert,  Dr.,  on  hybrid  Primulx, 
61. 

Heterostyled  plants,  illegitimate 
offspring  of,  188-244;  essential 
character  of,  245;  summary  of 
the  differences  of  fertility  be- 
tween legitimately  and  illegiti- 
mately fertilised  plants,  247; 
diameter  of  pollen-grains,  250  ; 
size  of  anthers,  structure  of  stig- 
ma, 253  ;  list  of  genera,  256 ;  ad- 
vantages derived  from  Hetero- 
stylism,  259  ;  means  by  which 
plants  became  heterostyled,  261 ; 
transmission  of  form,  269  ;  equal- 
styled  varieties,  273 ;  final  re- 
marks, 275. 

• dimorphic  plants,  14-54,  81- 

138. 

trimorphic  plants,  137-187. 

Hibiscus,  pollen-grains,  337. 

Hildebrand,  Prof.,  introduces  the 
word  "  heterostyled,"  2  ;  on  the 
ray-florets  of  the  Composite,  5, 6  ; 
Primula  Sinensis,  38,  40-42,  192, 
217  ;  Linum  (trandiflorum,  86,  87  ; 
L.  perenne,  92  ;  Pulmonaria  offi- 
cinalis,  101-103,  107,  239;  P. 
azurea,  110  ;  Polygonum  fagopy- 
rum,  111 ;  Oxalis,  169,  171-174, 
177,  181,  212-213,  321 ;  herma- 
phrodite plants  becoming  uni- 
sexual, 283 ;  Hordeum,  332. 

Homostyled  species  of  Primula.  49. 

Hooker,  Dr.,  on  Campanula,  329. 

Hordeum,  331. 

Hottonia  inflata,  53,  312. 

palustris,  50  ;  relative  fertility, 

52 ;  anthers  of,  253 ;  papillae  on 
stigma,  255. 

Houstonia  casrulea,  132,  255. 

Hoy  a  carnosa,  330. 

Hybrid  Primulas,  55-71. 

Hydrangea,  6,  7. 

Hypericinese,  123. 

Hyssopus  officinalis,  298. 


I. 


Hex  aguifolium,  297. 

opaca,  298. 

Illegitimate  offspring  of  hetero- 
styled plants,  188  ;  Lythrum  sali- 
caria,  dwarfed  stature  and  ster- 
ility, 192 ;  Oxalis,  transmission 
of  form  to  seedlings,  212 ;  Pri- 
mula sinensis,  in  some  degree 
dwarfed,  215  ;  equal-styled  va- 
rieties, 218-223  ;  Primula  vul- 
garis,  225  ;  transmission  of  form 
and  colour,  225  ;  seedlings,  227  ; 
P.  veris,  229 ;  dwarfed  stature 
and  sterility,  229-235;  equal- 
styled  varieties,  235,  239  ;  par- 
allelism between  illegitimate 
fertilisation  and  hybridism,  243. 

Tllecebrum,  310. 

Impatiens,  pollen-grains  of,  337. 

balsamina,  327. 

fulva,  326. 

noli-me-tangere,  327. 


J. 

Juglans  refiia,  10. 
Juncus  bufonius,  331,  342. 
Jussieu,   A.    de,   on   Malpighicese, 

0«Jft 


Kerner,  Prof.,  on  ray-florets,  6; 
Auricula,  43 ;  hybrid  forms  of 
Primula,  55,  73  ;  on  use  of  hairs 
within  the  corolla,  128;  size  of 
corolla  in  male  flowers,  308  ;  use 
of  glands  as  a  protection  to 
flowers,  330. 

Kirk,  Dr.,  on  Monochoria  vaginalis, 
330. 

Knoxia,  135. 

Koch  on  Primula  longiflora,  49. 

KrascheniniTcowia,  312. 

Kuhn,  Dr.,  on  cleistogamic  flow- 
ers, 3,  309,  310 ;  list  of  plants  pro- 
ducing differently  formed  seeds, 
9 ;  heterostyled  plants,  244 ;  Van- 
dellia  nummularifolia,  323 ;  V.  ses- 
siflora,  324. 


348 


INDEX. 


L  AGEBSTBCEMIA  . 

MULLEE. 

Lythrum  Grxfferi,  164. 

L. 

hyssopifolia,  165. 

salicaria,   116,   137  ;  power  of 

Lagerstrcemia  Indica,  167. 
parviflora,  167. 

mutual  fertilisation  between  the 
three  forms,  149-157;  summary 

regime,  167. 
Lathyrus  nissolia,  325,  341. 

of  results,  157-164;  illegitimate 
offspring  from  the  three  forms, 

Lecoq,  H.,  on  the  common  maple, 

191-203  ;  concluding  remarks  on, 

12;  cowslips  and  primroses,  57; 

203-211;   mid-styled  form,   241, 

Primula  elatior,  72  ;  Linum  Aus- 

258,  259,  280  ;  seeds,  249. 

triacum,  98  ;  Lythrum  hyssopifolia, 

thymifolia,  165. 

166;    Ehamnus,    296;    gynodice- 

cions  plants,  298  ;  Scabiosa  suc- 

cisa,  304  ;  Viola  odorata,  316. 

M. 

Lecrsia  orysoides,  332-334;  pollen- 

grains  of,  337. 

Malpighiacex,  330. 

Leggett,  Mr.,  Pontederia  cordata, 

Manettia  bicolor,  135. 

186. 

Maple,  the  common,  12. 

Legitimate   unions,   summary  on 
the  fertility  of  the  two,   com- 

Marshall, W.,  on  Primula  elatior, 
73  ;  Plantago  lanceolata,  306. 

pared  with  that  of  the  two  ille- 

Masters, Dr.  Maxwell,  on  cleisto- 

gitimate  in  Primula,  46-49  ;  fer- 

gamic flowers,  3. 

tility  of,  compared  with  illegiti- 

Maximowicz on  Krascheninikowia, 

mate,  247. 

312. 

Leighton,  Eev.  W.  A.,  on  the  cow- 

Meehan,  Mr.,   on    Mitchella,  285; 

slip  and  primrose,  56  ;  Verbascum 
virgatum,  78. 

Epigsea  repens,  297. 
Melissa  clinipodium,  298. 

Leontodon,  pollen-grains,  337. 

offidnalis,  298. 

Leptosiphon,  119. 

Mello,  Correa  de,  on  Arachis,  312; 

Leucosmia  acuminata,  114. 

Voandzeia,  326. 

Burnettiana,  114  ;  stigma,  254. 

Mentha  aquatica,  398. 

Lily,  the  Gloriosa,  146. 

hirsuta,  298. 

Limnanthemum  Indicum,  115  ;  pol- 
len-grains, 251  ;  anthers,  253. 

vulgaris,  298. 
Menyanthes,  310. 

Linaria  spuria,  324. 

trifoliata,  115. 

Lindley  on  Fragaria  elatior,  293. 
Linnaeus  on  Primula  veris,  vulgaris, 

Michalet  on  Oxalis  acetosella,  320  ; 
Linaria  spuria,  324. 

and  elatior,  56. 

Mitchella,  285. 

Linum  angustifolium,  100. 

repens,  125. 

Austriacum,  97. 

Mohl,   H.   von,    on   the    common 

catharticum,  100. 

cowslip,  14  ;  size  of  corolla  in  the 

corymbiferum,  100. 

sexes  of  the  same  species,  307  ; 

flavum,  81,  98;  stamens,  253. 

Trifolium  and  Arachis,  311  ;  cleis- 

grandiflorum,  81  ;  various  ex- 
periments, 87-89,  96  ;  pistils  and 

togamic  flower,  313,  341;  Oxalis 
acetosella,   320  ;    Impatiens  noli- 

stamens,  254,  255;  sterile  with 

me-tangere,  327  ;  Specularia  per- 

its  own-form  pollen,    264,   266, 

foliata,  329. 

267. 

Mollia  lepidota,  168. 

Lewisii,  101. 

—  —  speciosa  168. 

perenne,    90;    torsion  of  the 

Monnier,  M.,  on  Viola,  317. 

styles,  95  ;  long-styled  form,  97  ; 

Monochoria  vaginalis,  329. 

stigma,  248. 

Mulberry,  the,  10. 

salsoloides,  100. 
trigynum,  100. 

Miiller,  D.,  on  Viola  canina,  313. 
Miiller,  Fritz,  on  pollen  of  the  Vil- 

usitatissimum,  100. 
Lipostoma,  134. 
Lysimachia  vulgaris,  4,  341. 

larsia,    116;    Faramea,    129-131; 
Posoqueria  fraqrans,  131  ;  Nessea, 
166  ;  Oxalis,  179,  180  ;  Pontederia, 

INDEX. 


349 


MULLEB. 

PRIMULA. 

182-184;    Oxalis    Begnelli,    212; 
Chamissoa,  291. 

Oxalis  speciosa,  168,  175,  212. 
stricia.  181. 

Miiller,  H.,  on  the  frequency  of 

tropseoloides,  181. 

visits  by  insects  to  the  Umbelliferx 
and  Composites,  5  ;  on  dichogamy, 
10  ;  on  Anthophora  and  Bombylius 

Valdivmna,  170-172,  212. 
Oxlip,  the  Bardfield,  32,  72. 
,  the  common,  55  ;  differences 

sucking  the  cowslip,  22  ;  Primula 

in  structure   and   function    be- 

elatior, 32  ;  P.  villosa,  49  ;  Hottonia 

tween  the  two  parent  species,  56  ; 

palustris,  51  ;  table  of  relative  fer- 
tility of,  52  ;  Linum  catharticum, 
100;  Polygonum  fagopyrum,  112; 

effects  of  crossing,  60  ;  a  hybrid 
between  the  cowslip  and  prim- 
rose, 70. 

Lythrum  salicaria,   145;    on  the 

Oxybaphus,  312. 

origin  of  heterostylism,  264  ;  on 

the   Labiate,   298,   303;  Thymus 

serpyllum,  300  ;  Scabiosa  arvensis, 

P. 

304  ;  Plantago  lanceolata,  306  ;  size 

of  corolla  in  the  two  sexes  of  the 

Pseony,  pollen-grains  of,  337. 

same  species,  308  ;  Impatiens  bal- 
samina,  327  ;  Lysimachia,  342. 

Parallelism   between   illegitimate 
and  hybrid  fertilisation,  240. 

Myosotis,  307. 

Pavonia,  312. 

Phlox  Hentzii,  120. 

nivalis,  120. 

N. 

subulata,  120,  287. 

Planchon  on  Linum  salsoloides,  100  ; 

Nepeta  glechoma,  300. 

L.  Lewisii,  101  ;  on  Hugonia,  100. 

Nertera,  285. 

Plantago  lanceolata,  306. 

Nessea  verticillata,  166. 

media,  306. 

Nolana    prostrata,    variability   in 

Polemoniacese,  118. 

length  of  stamens  and  pistil,  262. 

Pollen-grains,  relative  diameter  of, 

Nydaginia,  312. 

250. 

Polyanthus,  18. 

Polygonacex,  111. 

0. 

Polygonum  bistorta,  113. 

fagopyrum,  111,   240  ;  pollen- 

Oldenlandia,  132. 

grains,  252. 

Oleacese,  117. 

Pontederia,  182  ;  pollen-grains,  185  ; 

Oliver,  Prof.,  on  ovules  of  Primula 

size  of  anthers,  253. 

veris,  17;  Viola,  317;  Campanula 

cordata,  186. 

colorata,  329. 

Posoqueria  fragrans,  131. 

Ononis  columnx,  324. 

Primrose,  the  common,  34,  57-71. 

minutissima,  325,  340. 

Primula,  the,  heterostyled  species 

parviflora,  325. 

of,    14  ;    summary    on,    45-49  ; 

Origanum  vulqare,  298. 
Oxalis  acetosella,  181;  pistil  of,  262; 

homostyled  species,  49. 
auricula,  30,  43,  48,  74,  223. 

cleistogamic  flowers,  320  ;  pollen- 

equal-styled  varieties,  273. 

grains,  337. 

cortusoides,  44. 

Bowii,  179. 

elata,  49. 

compressa,  178. 

elatior,  Jacq.,  32  ;  relative  fer- 

  corniculata,  181. 

tility  of  the  two  forms,  32,  47  ; 

Deppei,  179. 

not   a   hybrid,    72,    73;    equal- 

hedysaroides,  213. 
homostyled  species,  181. 

styled  var.  of,  224,  273. 
farinosa,     45  ;    equal-styled 

incarnata,  321. 

var.,  224,  273. 

Eegnelli,  173,  174,  212. 

hirsuta,  74. 

rosea,  177,  213. 

involucrata,  45. 

(Biophytum)  sensitiva,  180,  321  ; 
stigma,  254. 

lonqiflora,  49. 
moilis,  49,  50. 

350 


INDEX. 


PBIMULA. 

TEEVIRANUS. 

Primula  Scotica,  49,  50. 

Salcia  Horminum,  8. 

Sibirica,  49. 

Satureia  hortensis,  302,  304. 

Sikkimemis,  44,  47. 

Scabiosa  arvensis,  304. 

Sinensit,   22,   29,   38  ;  relative 

atro-purpurea,  305,  307. 

fertility,    39-43,    47,    48;    long- 

succisa,  305. 

styled,  213  ;    short-styled,   215  ; 

Scott,  J.,  on  Primula  auricula,  30, 

transmission  of  form,   constitu- 

43,   223;    P.  vulgaris,   34;   (var. 

tion  and  fertility,   216  ;    equal- 

rubra),  225  ;  P.  Sikkimensis,  44  ; 

styled  variety,  218-223,  273,  274. 
stricla,  50. 

P.  farinosa,  45,  224  ;  homostyled 
Primula;,  49,  50  :  hybrids,  74,  75  ; 

veris,  14  ;  difference  in  struc- 

length  of  pistil,   272;  Hottonia 

ture  between  the  two  forms,  15  ; 

palustris,    51  ;    Androsace    vital- 

degrees  of  fertility  when  legiti- 

liana, 53;  Polyanthus,   58;  Mit- 

mately  or  illegitimately  united, 
25-32  ;  fertility  possessed  by  ille- 
gitimate plants,  228-235  ;  equal- 
styled    red    variety,     235-239  ; 
long-styled,  242  ;  length  of  pistil, 

chella  repens,    127  ;    Acanthacete, 
312  ;  Eranthemum  ambiquum  bear- 
ing three  kinds  of  flowers,  328. 
Scrophularia  aquatica,  147. 
Serratula  tinctoria,  280,  306. 

262,  266. 

Sethia  acuminata,  123. 

verticillata,  49,  50. 

Sethia  obtusifolia,  123. 

vttlosa,  49. 

Smith,  Sir  J.  E.,  on  the  carrot,  8  ; 

vulgaris  (var.  acaulis  Linn.  ), 

hybrid    Verbascums,  76,  78;  Ser- 

34 ;  pollen-grains,    35  ;  relative 

ratula  tinctoria,  280  ;  Onicus,  306  ; 

fertility  of  the  two  forms,  36; 

Subularia,  310. 

length  of  pistil,  267. 

Soldanella  alpina,  54. 

Primula  vulgaris,  var.  rubra,  225- 

Specularia  perfoliata,  329. 

228. 

Spence,  Mr.,  on  Mollia,  168. 

Prunella  vulgaris,  298. 

Spermacoce,  135. 

Psyehotria,  135. 

Sprengel    on   Hottonia    palustris, 

Pulmonaria  angustifolia,  104,  240  ; 

50. 

anthers,  253,  287. 
azurea,  110. 

Stellaria  graminea,  312. 
Strawberry,  the  Hautbois,  293. 

officinalis,   101,   239  ;   number 

Subularia,  *310. 

of  flowers,  249  ;  pistil,  251. 

Suteria,  131. 

E. 

T. 

Ranunculus  aquatilis,  310. 

Thelymitra,  312. 

Ray-florets,  their  use,  5,  6. 
Rhamnus  catharticus,  293,  307  ;  size 

Thomson,  Dr.,  on  Campanula,  329. 
Thrum-eyed,  origin  of  term,  14. 

of  corolla,  308. 

Thwaites,  Mr.,  on  ovules  of  Lim- 

frangula,  296. 

nanthemum  Indicum,  115;  Sethia 

lanceolatus,  295. 

acuminata,     123;    Discospermum, 

Rhinanthus  crista-galli,  4. 

286. 

Rubiacese,  125,  131-136  ;  size  of  an- 

Thymelia, 114. 

thers,  253  ;  stigmas,  254  ;  number 

Thymus  citriodorus,  301. 

of  heterostyled  genera,  284-286. 

serpyllum,  299,  301,  304. 

Rudgea  eriantha,  135. 

vulgaris,  302. 

Rue,  the  common,  9. 

Timbal-Lagrave,  M.,  on   hybrids 

Ruellia  tuberosa,  328. 

in  genus  Cistus,  76. 

Torrey,  Dr.,   on  Hottonia  inflata, 

53,  312. 

S. 

Transmission  of  the  two  forms  of 

heterostyled  plants,  269-270. 

Salvia,  307. 

Treviranus  on  Androsace  vitalliana, 

cleistogama,  339. 

53  ;  Linum,  81. 

INDEX. 


351 


VANDELLIA. 


V. 

Vandellia  nummulari folia,  323. 

sessiflora,  324. 

Vaucher  on  the  carrot,  8 ;  Solda- 
nella^alpina,  54;  Lythrum  sali- 
caria,  138,  144;  L.  thymifolia, 
165  ;  Ilex  aquifolium,  297 ;  on 
Labiatie,  298;  Viola  hirta  and 
collina,  316. 

Verbascum,  wild  hybrids  of,  75- 
80. 

lychnitis,  30,  76-78. 

phazniceum,  78. 

thapsus,  76-79. 

virgatum,  78. 

Viburnum,  6,  7. 

Vicia,  326. 

Villarsia,  116 ;  anthers,  252. 

Kioto  alba,  314,  319. 

bicolor,  319. 

biflora,  319. 

conina,  313,  320. 

collina,  316. 

rfafior,  319. 

hirta,  317,  319. 

ionodittm,  319. 


WKAY. 

Fioto  Zawci/oZia,  319. 

mirabilis,  319. 

nawa,  318,  319 ;  pollen-grains 

of,  337. 

odorata,  316,  335. 

palustris,  319. 

Roxburghiana,  318. 

Ruppii,  319. 

sylvatica,  319. 

tricolor,  319. 

Foawdseio,  326. 


W. 

Walnut,  the,  10. 

Watson,  H.  C.,  on  cowslips,  prim- 
roses, and  oxlips,  57,  60,  63; 
Primida  elatior,  72,  73. 

Weddell,  Dr.,  on  hybrids  between 
Aceras  and  Orchis,  76. 

Wetterhan,  Mr.,  on  Corylus,  10. 

Wichura,  Max,  on  hybrid  willows, 
76 ;  sterile  hybrids,  241. 

Wirtgen  on  Lythrum  salicaria,  138, 
144,  148. 

Wooler,  W.,  on  Polyanthus,  18. 

Wray,  Leonard,  on  Fragaria,  293. 


THE  EXD. 


LIBRARY 


This  book  is  DUElfia  the  last  date  stamped  beloi 


926^ 


1899 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 

IBIIBi 

AA    000777198    3 


